Revert "g-i: change g-ir-scanner arg --library=libgstfoo-X.la to --library=gstfoo-X"

Revert "g-i: change g-ir-scanner arg --library=libgstfoo-X.la to --library=gstfoo-X"

This reverts commit e39fbe6b7e14ccccbf47a5726a18eb963535063b.

Looks like we need to pass the full .la file after all in a setup
with libtool, or it might not find the library, e.g. like

  ERROR: can't resolve libraries to shared libraries: gstfft-1.0

Conflicts:
	gst-libs/gst/audio/Makefile.am
	gst-libs/gst/pbutils/Makefile.am

Also see https://bugzilla.gnome.org/show_bug.cgi?id=603710