remove `ImplicitUsings disable` from projects (part 5) (#3989)

* remove ImplicitUsings disable from projects.
ZPages

* Hosting

* Propagators

src/OpenTelemetry.Exporter.ZPages/Implementation/ZPagesActivityAggregate.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Diagnostics;
 
 namespace OpenTelemetry.Exporter.ZPages.Implementation

src/OpenTelemetry.Exporter.ZPages/Implementation/ZPagesActivityTracker.cs

@@ -14,9 +14,7 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Collections.Concurrent;
-using System.Collections.Generic;
 using System.Timers;
 
 namespace OpenTelemetry.Exporter.ZPages.Implementation

src/OpenTelemetry.Exporter.ZPages/Implementation/ZPagesExporterEventSource.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Diagnostics.Tracing;
 using OpenTelemetry.Internal;
 

src/OpenTelemetry.Exporter.ZPages/OpenTelemetry.Exporter.ZPages.csproj

@@ -8,7 +8,6 @@
 
     <!-- this is temporary. will remove in future PR. -->
     <Nullable>disable</Nullable>
-    <ImplicitUsings>disable</ImplicitUsings>
   </PropertyGroup>
 
   <ItemGroup>

src/OpenTelemetry.Exporter.ZPages/ZPagesExporterHelperExtensions.cs

@@ -14,8 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
-
 using OpenTelemetry.Exporter.ZPages;
 using OpenTelemetry.Internal;
 

src/OpenTelemetry.Exporter.ZPages/ZPagesExporterStatsHttpServer.cs

@@ -14,12 +14,8 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Collections.Concurrent;
-using System.IO;
 using System.Net;
-using System.Threading;
-using System.Threading.Tasks;
 using OpenTelemetry.Exporter.ZPages.Implementation;
 using OpenTelemetry.Internal;
 

src/OpenTelemetry.Exporter.ZPages/ZPagesProcessor.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Diagnostics;
 using OpenTelemetry.Exporter.ZPages.Implementation;
 using OpenTelemetry.Trace;

src/OpenTelemetry.Extensions.Hosting/Implementation/HostingExtensionsEventSource.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Diagnostics.Tracing;
 using OpenTelemetry.Internal;
 

src/OpenTelemetry.Extensions.Hosting/Implementation/TelemetryHostedService.cs

@@ -14,10 +14,7 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Diagnostics;
-using System.Threading;
-using System.Threading.Tasks;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using OpenTelemetry.Metrics;

src/OpenTelemetry.Extensions.Hosting/Metrics/MeterProviderBuilderExtensions.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace OpenTelemetry.Metrics

src/OpenTelemetry.Extensions.Hosting/OpenTelemetry.Extensions.Hosting.csproj

@@ -7,7 +7,6 @@
 
     <!-- this is temporary. will remove in future PR. -->
     <Nullable>disable</Nullable>
-    <ImplicitUsings>disable</ImplicitUsings>
   </PropertyGroup>
 
   <ItemGroup>

src/OpenTelemetry.Extensions.Hosting/OpenTelemetryServicesExtensions.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Hosting;
 using OpenTelemetry.Extensions.Hosting.Implementation;

src/OpenTelemetry.Extensions.Hosting/Trace/TracerProviderBuilderExtensions.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace OpenTelemetry.Trace

src/OpenTelemetry.Extensions.Propagators/B3Propagator.cs

@@ -14,10 +14,7 @@
 // limitations under the License.
 // </copyright>
 
-using System;
-using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using System.Text;
 using OpenTelemetry.Context.Propagation;
 using OpenTelemetry.Internal;

src/OpenTelemetry.Extensions.Propagators/JaegerPropagator.cs

@@ -14,10 +14,7 @@
 // limitations under the License.
 // </copyright>
 
-using System;
-using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using OpenTelemetry.Context.Propagation;
 using OpenTelemetry.Internal;
 

src/OpenTelemetry.Extensions.Propagators/OpenTelemetry.Extensions.Propagators.csproj

@@ -9,7 +9,6 @@
 
     <!-- this is temporary. will remove in future PR. -->
     <Nullable>disable</Nullable>
-    <ImplicitUsings>disable</ImplicitUsings>
   </PropertyGroup>
 
   <ItemGroup>

src/OpenTelemetry.Extensions.Propagators/OpenTelemetryPropagatorsEventSource.cs

@@ -14,7 +14,6 @@
 // limitations under the License.
 // </copyright>
 
-using System;
 using System.Diagnostics.Tracing;
 
 namespace OpenTelemetry.Internal