Remove @Overridable from CompatChange flag

Since the change is also flag guarded there is no need for the change to
be overridable.

Bug: 311435342
test: atest CtsAppCompatHostTestCases:com.android.cts.appcompat.CompatChangesValidConfigTest#testOnlyAllowedlistedChangesAreOverridable
Change-Id: If3831072343836ecae3ed83f1116892224aefa53
1 file changed