render: stop auto-creating wl_drm

wl_drm is a legacy interface superseded by the linux-dmabuf
protocol. All clients should migrate.

As a first step, stop creating the wl_drm global by default.
This should let us discover any remaining issues in clients.
Compositors can still manually create the global if they want to.
As a second step, we can completely drop our implementation.

render/wlr_renderer.c

@@ -95,14 +95,9 @@ bool wlr_renderer_init_wl_display(struct wlr_renderer *r,
 	}
 
 	if (wlr_renderer_get_dmabuf_texture_formats(r) != NULL &&
-			wlr_renderer_get_drm_fd(r) >= 0) {
-		if (wlr_drm_create(wl_display, r) == NULL) {
-			return false;
-		}
-
-		if (wlr_linux_dmabuf_v1_create_with_renderer(wl_display, 4, r) == NULL) {
-			return false;
-		}
+			wlr_renderer_get_drm_fd(r) >= 0 &&
+			wlr_linux_dmabuf_v1_create_with_renderer(wl_display, 4, r) == NULL) {
+		return false;
 	}
 
 	return true;