images filter: remove the redundant inverted filter

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)

docs/sources/reference/commandline/cli.rst

@@ -687,7 +687,6 @@ The filtering flag (-f or --filter) format is of "key=value". If there are more
 than one flag, then either semi-colon delimit (";"), or pass multiple flags.
 
 Current filters:
- * tagged (boolean - true or false)
  * untagged (boolean - true or false)
 
 
@@ -697,7 +696,7 @@ Filtering for untagged images
 
 .. code-block:: bash
 
-    $ sudo docker images --filter "tagged=false"
+    $ sudo docker images --filter "untagged=true"
 
     REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
     <none>              <none>              8abc22fbb042        4 weeks ago         0 B

server/server.go

@@ -707,9 +707,6 @@ func (srv *Server) Images(job *engine.Job) engine.Status {
 	if i, ok := imageFilters["untagged"]; ok && strings.ToLower(i) == "true" {
 		filt_tagged = false
 	}
-	if i, ok := imageFilters["tagged"]; ok && strings.ToLower(i) == "false" {
-		filt_tagged = false
-	}
 
 	if job.GetenvBool("all") && !filt_tagged {
 		allImages, err = srv.daemon.Graph().Map()