gbm: remove never-implemented function

I assume this was implemented in a previous version of that commit, but
was removed in the version that actually landed.

Fixes: 8430af5ebe "Add support for swrast to the DRM EGL platform"
Cc: Giovanni Campagna <gcampagna@src.gnome.org>
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/gbm/gbm-symbols-check

@@ -40,7 +40,6 @@ gbm_bo_get_user_data
 gbm_bo_destroy
 gbm_surface_create
 gbm_surface_create_with_modifiers
-gbm_surface_needs_lock_front_buffer
 gbm_surface_lock_front_buffer
 gbm_surface_release_buffer
 gbm_surface_has_free_buffers

src/gbm/main/gbm.h

@@ -386,8 +386,6 @@ gbm_surface_create_with_modifiers(struct gbm_device *gbm,
                                   uint32_t format,
                                   const uint64_t *modifiers,
                                   const unsigned int count);
-int
-gbm_surface_needs_lock_front_buffer(struct gbm_surface *surface);
 
 struct gbm_bo *
 gbm_surface_lock_front_buffer(struct gbm_surface *surface);