git: remove unneeded volatiles

Message start marker, message end marker, the files are all received
from the same thread (either stdout or stderr) => although the listener
is listening to different threads, in fact only one thread is important
during the command execution.

Follow-up to 712a158

plugins/git4idea/src/git4idea/commands/GitMessageWithFilesDetector.java

@@ -42,8 +42,8 @@ public class GitMessageWithFilesDetector implements GitLineHandlerListener {
   @NotNull private final VirtualFile myRoot;
 
   @NotNull protected final Set<String> myAffectedFiles = new HashSet<>();
-  protected volatile boolean myMessageDetected;
-  @Nullable private volatile Key myMessageOutputType;
+  protected boolean myMessageDetected;
+  @Nullable private Key myMessageOutputType;
 
   public GitMessageWithFilesDetector(@NotNull Event event, @NotNull VirtualFile root) {
     myEvent = event;