In ClosingFuture, remove a workaround for [JDK-7101822](https://bugs.openjdk.java.net/browse/JDK-7101822)(?) now that we [build with a JDK after JDK 8](#6549). This follows up on cl/332225001 and cl/643394004.

RELNOTES=n/a
PiperOrigin-RevId: 706691218

Author: cpovirk

android/guava/src/com/google/common/util/concurrent/ClosingFuture.java

@@ -1223,9 +1223,7 @@ private Peeker(ImmutableList<ClosingFuture<?>> futures) {
    *           .closing(executor);
    * }</pre>
    */
-  // TODO(cpovirk): Use simple name instead of fully qualified after we stop building with JDK 8.
-  @com.google.errorprone.annotations.DoNotMock(
-      "Use ClosingFuture.whenAllSucceed() or .whenAllComplete() instead.")
+  @DoNotMock("Use ClosingFuture.whenAllSucceed() or .whenAllComplete() instead.")
   public static class Combiner {
 
     private final CloseableList closeables = new CloseableList();

guava/src/com/google/common/util/concurrent/ClosingFuture.java

@@ -1228,9 +1228,7 @@ private Peeker(ImmutableList<ClosingFuture<?>> futures) {
    *           .closing(executor);
    * }</pre>
    */
-  // TODO(cpovirk): Use simple name instead of fully qualified after we stop building with JDK 8.
-  @com.google.errorprone.annotations.DoNotMock(
-      "Use ClosingFuture.whenAllSucceed() or .whenAllComplete() instead.")
+  @DoNotMock("Use ClosingFuture.whenAllSucceed() or .whenAllComplete() instead.")
   public static class Combiner {
 
     private final CloseableList closeables = new CloseableList();