graphics/poppler-glib: disable gkt-test/demo builds

In unclean build environments GTK could get picked up and lead to linker errrors
in demo applications which are not installed, but still manage to make the build
fail.

Remove the temporary work around added in r523840 which passed -L${LOCALBASE}/lib
to the linker.

PR: 243525
Reported by: Walter Schwarzenfeld <w.schwarzenfeld@utanet.at>, O. Hartmann <ohartmann@walstatt.org>