Revert "CodeGen: MachineInstr::getIterator() => getInstrIterator(), NFC"

This reverts commit r261504, since it's not obvious the new name is
better:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160222/334298.html

I'll recommit if we get consensus that it's the right direction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261567 91177308-0d34-0410-b5e6-96231b3b80d8
27 files changed