qga/vss-win32: fix midl arguments

qga/vss-win32: fix midl arguments

Microsoft midl compiler doesn't take "-options" form, nor does it take
OUTPUT filename. The -I option seems needless as well (at least with
VS15).

It's not clear what was actually used when it was introduced in commit
b39297aedfabe9.

strings says "Created by MIDL version 7.00.0555 at Fri Dec 21 13:36:39
2012".

I doubt the makefile rule actually ever worked.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>