fsck-objects: Remove --standalone

fsck-objects: Remove --standalone

The fsck-objects command (back then it was called fsck-cache)
used to complain if objects referred to by files in .git/refs/
or objects stored in files under .git/objects/??/ were not found
as stand-alone SHA1 files (i.e.  found in alternate object pools
or packed archives stored under .git/objects/pack).  Back then,
packs and alternates were new curiosity and having everything as
loose objects were the norm.

When we adjusted the behaviour of fsck-cache to consider objects
found in packs are OK, we introduced the --standalone flag as a
backward compatibility measure.

It still correctly checks if your repository is complete and
consists only of loose objects, so in that sense it is doing the
"right" thing, but checking that is pointless these days.  This
commit removes --standalone flag.

See also:

	23676d407c63a6f67f8ce3ff192199bda03e6a03
	8a498a05c3c6b2f53db669b24f36257ab213eb4c

Signed-off-by: Junio C Hamano <junkio@cox.net>