[analyzer][NFC] Remove "V2" from ArrayBoundCheckerV2.cpp (#126094)
Previously commit 6e17ed9b04e5523cc910bf171c3122dcc64b86db deleted the
obsolete checker `alpha.security.ArrayBound` which was implemented in
`ArrayBoundChecker.cpp` and renamed the checker
`alpha.security.ArrayBoundV2` to `security.ArrayBound`.
This commit concludes that consolidation by renaming the source file
`ArrayBoundCheckerV2.cpp` to `ArrayBoundChecker.cpp` (which was "freed
up" by the previous commit).