(This is a merge of http://go/wvgerrit/65263)
Now that C++11 is mandatory, we can drop the OVERRIDE macro which was
inconsistently used in the codebase in favor of using the override
keyword directly.
Bug: 111851141
Test: CE CDM Unit Tests
Test: Android Build
Change-Id: I0b7559624b84feb19740afd63463dadd243412b0