extensionUtils: Remove version check for js-version

This is seldomly used, and isn't checked in SweetTooth. Just remove
this inconsistency here rather than adding infrastructure to manage
and check it elsewhere.

https://bugzilla.gnome.org/show_bug.cgi?id=677586

js/misc/config.js.in

@@ -4,8 +4,6 @@
 const PACKAGE_NAME = '@PACKAGE_NAME@';
 /* The version of this package */
 const PACKAGE_VERSION = '@PACKAGE_VERSION@';
-/* The version of GJS we're linking to */
-const GJS_VERSION = '@GJS_VERSION@';
 /* 1 if gnome-bluetooth is available, 0 otherwise */
 const HAVE_BLUETOOTH = @HAVE_BLUETOOTH@;
 /* gettext package */