compositor: free region members on surface destroy
compositor: free region members on surface destroy

The two pixman regions of struct wlsc_surface were not being freed
properly.

Fixes some Valgrind errors.

Signed-off-by: Pekka Paalanen <6c0263d81461c956d504307112a4ce25eaacc3d1@gmail.com>

mchalupa/weston,Gnurou/weston,eyolfson/weston,Fantu/compositor-spice,krezovic/weston,jonnylamb/weston,krezovic/weston,Tarnyko/weston-xdg_surface_present,udoprog/weston,giucam/weston,sir-murray/weston,Fantu/compositor-spice,eyolfson/weston,Fantu/compositor-spice,xorgy/weston,Tarnyko/weston-xdg_surface_present,giucam/weston,udoprog/weston,xorgy/weston,kwm81/weston,mchalupa/weston,jonnylamb/weston,kwm81/weston,sir-murray/weston,Gnurou/weston