MS inline asm: remove obsolete code adding AOK_SizeDirective (e.g. dword ptr)

The AOK_SizeDirective part from 5b37c181
(2014-08) seems unneeded nowadays (the root cause has likely been fixed
elsewhere). The part abuses that `call dword ptr foo` assembles the same way as `call
foo` in Intel syntax, which is going to be fixed (changed) by D149579.

The generated object files for
CodeGen/ms-inline-asm{,-functions,-variables,-static-variable}.c and
CodeGenCXX/ms-inline-asm-fields.cpp are unchanged
(-mno-incremental-linker-compatible) with just this patch. When D149579 is
subsequently applied, the FIXME part of `kptr` in
CodeGen/ms-inline-asm-functions.c will be fixed.

Differential Revision: https://reviews.llvm.org/D149695