gconf: fix the "unshipped files" warnings

1) correct static libs removal in do_install_append
2) provide .la files in -dev package as it's usually done in other
packages.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>