run-js-test: link to libgnome-shell.la

The tests were broken again, because since Shell-0.1.gir now has
'shared-library="libgnome-shell.so"', the references to Shell.PerfLog
ended up pulling in libgnome-shell in addition to the copy of
shell-perf-log.c that libjs-test was built with.

Fix all this hopefully forever by just making run-js-test link to
libgnome-shell.

https://bugzilla.gnome.org/show_bug.cgi?id=649203