wayland: Remove unused function
wayland: Remove unused function

The function force_roundtrip was unused and required API that was
removed from Wayland.

Reviewed-by: Robert Bragg <12e9293ec6b30c7fa8a0926af42807e929c1684f@linux.intel.com>

djdeath/cogl-android,gcampax/cogl,djdeath/cogl,gcampax/cogl,Distrotech/cogl,djdeath/cogl,gcampax/cogl,djdeath/cogl-android,Distrotech/cogl,djdeath/cogl-android,djdeath/cogl,collects/cogl,gcampax/cogl,Distrotech/cogl,collects/cogl,Distrotech/cogl