Eliminate misleading warning.

Remove token from deferred list of tokens to be removed once token
is removed. Leaving it in the list leads to logging messages like
"WindowManager: removeAppFromTaskLocked: token=AppWindowToken{...
} not found" when an attempt to remove it a second time fails.

Discovered in logs from b/17512377.

Change-Id: Ic83d81841b9b74ae5c4c433d1086d3bbda8e1d64

services/core/java/com/android/server/wm/DisplayContent.java

@@ -328,6 +328,7 @@ class DisplayContent {
                     for (int tokenNdx = tokens.size() - 1; tokenNdx >= 0; --tokenNdx) {
                         AppWindowToken wtoken = tokens.get(tokenNdx);
                         if (wtoken.mDeferRemoval) {
+                            stack.mExitingAppTokens.remove(wtoken);
                             wtoken.mDeferRemoval = false;
                             mService.removeAppFromTaskLocked(wtoken);
                         }