libgc: Drop, its bdwgc in OE-Core

There is not point in having two of this piece of software, I've merged
the missing PACKAGECONFIG into the OE-Core version, we can drop this one.

Update zile's DEPENDS to match (its only user in meta-oe).

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>