Remove the jhbuild wrapper script

It's mostly equivalent to "jhbuild run gnome-shell", which is
the preferred way. Also, running from the source tree can't be
supported at this point, and the wrapper is getting in the way
of having two binaries, one for wayland and one for X11.

https://bugzilla.gnome.org/show_bug.cgi?id=705497
Implementing building two separate binaries for x11 and wayland

Build gnome-shell for x11, and gnome-shell-wayland for wayland
(as well as the associated libgnome-shell and libgnome-shell-wayland).
The first one links to libmutter, the second to libmutter-wayland.

libgnome-shell and libgnome-shell-wayland are now compiled from
libgnome-shell-base (with all sources that are independent of mutter),
libgnome-shell-menu (with the copy-pasted gtk sources), plus the
sources that use mutter API

https://bugzilla.gnome.org/show_bug.cgi?id=705497