style: Remove remaining deprecated MALLOC/FREE macros

Mechanically replace uses of MALLOC/FREE with appropriate invocations of
malloc(9) / free(9) (a series of sed expressions). Something like:

• MALLOC(a, b, ... -> a = malloc(...
• FREE( -> free(
• free((caddr_t) -> free(

No functional change.

For now, punt on modifying contrib ipfilter code, leaving a definition of
the macro in its KMALLOC().

Reported by: jhb
Reviewed by: cy, imp, markj, rmacklem
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14035