Remove superfluous non-operands from LDXR, STXR, and related instructions on AArch64
On AArch64 we have superfluous operands in the exclusive load and store instructions in DR's IR:
0x0000ffff7d459b24 885f7c01 ldxr (%x0)[4byte] $0x1f $0x1f -> %w1
0x0000ffff7d459af0 885ffc01 ldaxr (%x0)[4byte] $0x1f $0x1f -> %w1
0x0000ffff7d459afc 88027c04 stxr %w4 $0x1f -> (%x0)[4byte] %w2
0x0000ffff7d459b28 8803fc02 stlxr %w2 $0x1f -> (%x0)[4byte] %w3
These 0x1f
integers seem to be just part of the encoding and aren't actually operands. I would expect them to not show up in the IR at all.