package/mesa3d: drop pkgconfig workaround

This workaround is not needed as of commit
5cff3a8b which properly sets the
PKG_CONFIG_LIBDIR for native: true dependencies.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>