Refix aborts due to GC losing pseudovectors

Refix aborts due to GC losing pseudovectors

This is simpler, and fixes a bug in the previous fix.
* src/alloc.c (MALLOC_ALIGNMENT_BOUND): Simplify by
using max_align_t, since the buggy implementations won’t
break this simpler implementation.
(LISP_ALIGNMENT): Simplify by just using GCALIGNMENT, since the
fancier implementation wasn’t correct anyway, and fixing it
isn’t worth the trouble on practical platforms.
* src/lisp.h (union emacs_align_type): Remove.