Remove LOCAL_LIB_DIRS warning added in r275839.

The case for which this was added, r274807, causes this warning to
always show. LOCAL_DIRS=foo LOCAL_LIB_DIRS=foo/lib. The only case in
which r274807 is a problem is if foo/Makefile does not contain
SUBDIR+=lib, which is a normal convention. LOCAL_LIB_DIRS is a special
hack only to get a library into the _generic_libs list for the
'make libraries' bootstrapping phase. The old behavior changed in
r274807 was only in head during the 10.0 cycle, so the warning was
only ever needed until release anyhow.

Reported by: ngie
MFC after: 1 week
Sponsored by: Dell EMC Isilon