Revert "For the ARM integrated assembler add checking of the alignments on vld/vst instructions.  And report errors for alignments that are not supported."

It doesn't build with MSVC 2012, because MSVC doesn't allow union
members that have non-trivial default constructors.  This change added
'SMLoc AlignmentLoc' to MemoryOp, which made MemoryOp's default ctor
non-trivial.

This reverts commit r205930.