[MemOperands] Clarify code around dropping memory operands [NFC]

Clarify a comment about what it means to drop memory operands from an instruction.  While I'm adding change the name of the method slightly to make it a bit more clear what's going on when reading calling code.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256346 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed