[BOLT] Strip redundant AdSize override prefix

Since LLVM MC now preserves redundant AdSize override prefix (0x67), remove it
in BOLT explicitly (-x86-strip-redundant-adsize, on by default).

Test Plan:
`bin/llvm-lit -a bolt/test/X86/addr32.s`

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D120975