ReplicatedPG: simplify getattrs_maybe_cache()

Nobody calls getattrs_maybe_cache without specifying user_only, so remove
the option and do filtering unconditionally. While we're there, remove the
if(out) branches, because the out map is definitely required (the
functions we call dereference it without checking).

Signed-off-by: Greg Farnum <greg@inktank.com>
FileStore: remove dead code

This case wasn't reachable when it was introduced, and it's still not.

Signed-off-by: Greg Farnum <greg@inktank.com>
FileStore: do not use user_only in collection_getattrs

There's no particular reason why any of the callers of collection_getattrs
want to avoid looking at Ceph's internal xattrs.
It looks like this flag (set in 1862ddd88548fd4609f4fa9715dbad42a84d3775) was
set this way by mistake.
And finally, we don't actually set xattrs on collections anymore, anyway.

Signed-off-by: Greg Farnum <greg@inktank.com>