Remove acl_size.c; apparently it was never used.

PR:		194398
Submitted by:	ngie@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Make the auto_master(5) man page clearer on how auto_master
and map files work together, and add example for smbfs.

Differential Revision:	https://reviews.freebsd.org/D1184
Reviewed by:	wblock@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation