Remove more dead code now that this is only used for inline asm.

MO_ConstantPoolIndex is handled in printLeaMemReference.
MO_JumpTableIndex and MO_ExternalSymbol don't show up in inline asm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195847 91177308-0d34-0410-b5e6-96231b3b80d8