AOSP/Messaging - Update language to comply with Android's inclusive language guidance.

See https://source.android.com/setup/contribute/respectful-code for reference

BUG=161896447

Test: make and make messagingtests
Change-Id: I01c520f1d5e9eab8dbb25b08d133ae34bd301093

src/com/android/messaging/util/Trace.java

@@ -101,7 +101,7 @@ public final class Trace {
     }
 
     /**
-     * Dummy class that we use if we aren't really tracing.
+     * Placeholder class that we use if we aren't really tracing.
      */
     private static final class TraceShim extends AbstractTrace {
         @Override