render/gles2: remove stale gles2_texture_from_wl_drm() prototype

This function doesn't exist anymore.

include/render/gles2.h

@@ -126,8 +126,6 @@ struct wlr_gles2_renderer *gles2_get_renderer(
 struct wlr_gles2_texture *gles2_get_texture(
 	struct wlr_texture *wlr_texture);
 
-struct wlr_texture *gles2_texture_from_wl_drm(struct wlr_renderer *wlr_renderer,
-	struct wl_resource *data);
 struct wlr_texture *gles2_texture_from_buffer(struct wlr_renderer *wlr_renderer,
 	struct wlr_buffer *buffer);
 void gles2_texture_destroy(struct wlr_gles2_texture *texture);