Enable akka instrumentation by default

dd-java-agent/instrumentation/akka-http-10.0/src/main/scala/datadog/trace/instrumentation/akkahttp/AkkaHttpClientInstrumentation.java

@@ -42,11 +42,6 @@ public final class AkkaHttpClientInstrumentation extends Instrumenter.Default {
     super("akka-http", "akka-http-client");
   }
 
-  @Override
-  protected boolean defaultEnabled() {
-    return false;
-  }
-
   @Override
   public ElementMatcher<TypeDescription> typeMatcher() {
     return named("akka.http.scaladsl.HttpExt");

dd-java-agent/instrumentation/akka-http-10.0/src/main/scala/datadog/trace/instrumentation/akkahttp/AkkaHttpServerInstrumentation.java

@@ -40,11 +40,6 @@ public final class AkkaHttpServerInstrumentation extends Instrumenter.Default {
     super("akka-http", "akka-http-server");
   }
 
-  @Override
-  protected boolean defaultEnabled() {
-    return false;
-  }
-
   @Override
   public ElementMatcher<TypeDescription> typeMatcher() {
     return named("akka.http.scaladsl.HttpExt");

dd-java-agent/instrumentation/akka-http-10.0/src/test/groovy/AkkaHttpClientInstrumentationTest.groovy

@@ -22,9 +22,6 @@ import static datadog.trace.agent.test.asserts.ListWriterAssert.assertTraces
 import static datadog.trace.agent.test.server.http.TestHttpServer.httpServer
 
 class AkkaHttpClientInstrumentationTest extends AgentTestRunner {
-  static {
-    System.setProperty("dd.integration.akka-http-client.enabled", "true")
-  }
 
   private static final String MESSAGE = "an\nmultiline\nhttp\nresponse"
   private static final long TIMEOUT = 10000L

dd-java-agent/instrumentation/akka-http-10.0/src/test/groovy/AkkaHttpServerInstrumentationTest.groovy

@@ -9,9 +9,6 @@ import spock.lang.Shared
 import static datadog.trace.agent.test.asserts.ListWriterAssert.assertTraces
 
 class AkkaHttpServerInstrumentationTest extends AgentTestRunner {
-  static {
-    System.setProperty("dd.integration.akka-http-server.enabled", "true")
-  }
 
   @Shared
   int asyncPort