wayland-surface: Cleanup properly in _dispose
wayland-surface: Cleanup properly in _dispose

When disposing a ClutterWaylandSurface we now make sure to unref any
pipeline we created and unref any surface buffer textures we created.

Reviewed-by: Neil Roberts <822ec91a7ef82248fd36162ca8ac3283eba70848@linux.intel.com>
Reviewed-by: Emmanuele Bassi <049ee2061f71220e5aaf33f5be422fc2a2b06a44@linux.intel.com>

collects/clutter,collects/clutter,djdeath/clutter-android,heysion/clutter-clone,jigpu/clutter,collects/clutter,djdeath/clutter-multithreaded,djdeath/clutter-android,djdeath/clutter,ebassi/clutter,djdeath/clutter-multithreaded,heysion/clutter-clone,collects/clutter,jigpu/clutter,Distrotech/clutter,djdeath/clutter,Distrotech/clutter,djdeath/clutter-multithreaded,jigpu/clutter,ebassi/clutter,Distrotech/clutter,djdeath/clutter,ebassi/clutter,kerrickstaley/clutter-vala,heysion/clutter-clone,kerrickstaley/clutter-vala,GNOME/clutter,jigpu/clutter,kerrickstaley/clutter-vala,GNOME/clutter,GNOME/clutter,djdeath/clutter,heysion/clutter-clone,Distrotech/clutter,djdeath/clutter,ebassi/clutter,Distrotech/clutter,GNOME/clutter,djdeath/clutter,ebassi/clutter,jigpu/clutter,djdeath/clutter-android,GNOME/clutter,kerrickstaley/clutter-vala,jigpu/clutter,heysion/clutter-clone,collects/clutter,djdeath/clutter-multithreaded,Distrotech/clutter,djdeath/clutter-android,djdeath/clutter-android