configure: Remove a xcb-dri2 leftover
configure: Remove a xcb-dri2 leftover

Fixes compositor and clients trying to link against xcb-dri2.

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