bsd.lib.mk: Simplify CLEANFILES handling.

bsd.lib.mk: Simplify CLEANFILES handling.

This limits CLEANFILES removal to just bsd.obj.mk now and removes the need
for NOPATH_FILES.

This reverts r96529 which was done due to the command line being too long
for libc.  Since then all architectures now use 256k for ARG_MAX (r170102).
Regardless of that, the libc CLEANFILES is only 72k now.  Others
may be larger but not likely to hit the limit.  If needed, we can improve
the bsd.obj.mk clean: target to split up the list via bmake features.

This also removes some workarounds that are no longer needed.
- a.out removal
- OBJS.tmp, which has not been needed since r117080.
- *.so, which has not been needed since a .so->.So rename in r42450.

This also fixes STATICOBJS and SHLIB_LINK not being in the .NOPATH list.

Sponsored by:	EMC / Isilon Storage Division