deskutils/py-spice-gtk: remove port

spice-gtk dropped support of the old style Python bindings (non-gir based)
quite some time ago [1]. So keeping this port no longer makes sense as
it's not different from the master port.

1: https://github.com/SPICE/spice-gtk/commit/0917002c48a0a5deb615d120a0e5997eefc89fd4