remove unused imports and only request 1 inner observable in onStart

Author: davidmoten

src/main/java/rx/internal/operators/OperatorConcat.java

@@ -110,9 +110,8 @@ public void call() {
 
         @Override
         public void onStart() {
-            // no need for more than 1 at a time since we concat 1 at a time, so we'll request 2 to start ...
-            // 1 to be subscribed to, 1 in the queue, then we'll keep requesting 1 at a time after that
-            request(2);
+            // no need for more than 1 at a time
+            request(1);
         }
 
         private void requestFromChild(long n) {

src/test/java/rx/internal/operators/OperatorConcatTest.java

@@ -36,9 +36,7 @@
 import org.mockito.InOrder;
 
 import rx.Observable.OnSubscribe;
-import rx.Scheduler.Worker;
 import rx.*;
-import rx.functions.Action0;
 import rx.functions.Func1;
 import rx.internal.util.RxRingBuffer;
 import rx.observers.TestSubscriber;