Use 'final' and 'override' specifiers directly in ART.

Remove all uses of macros 'FINAL' and 'OVERRIDE' and replace them with
'final' and 'override' specifiers. Remove all definitions of these
macros as well, which were located in these files:
- libartbase/base/macros.h
- test/913-heaps/heaps.cc
- test/ti-agent/ti_macros.h

ART is now using C++14; the 'final' and 'override' specifiers have
been introduced in C++11.

Test: mmma art
Change-Id: I256c7758155a71a2940ef2574925a44076feeebf