examples: use NULL theme name instead of "default"

This leaves it up to wlr_xcursor_theme_load() to pick the theme
name.

examples/multi-pointer.c

@@ -293,7 +293,7 @@ int main(int argc, char *argv[]) {
 
 	clock_gettime(CLOCK_MONOTONIC, &state.last_frame);
 
-	struct wlr_xcursor_theme *theme = wlr_xcursor_theme_load("default", 16);
+	struct wlr_xcursor_theme *theme = wlr_xcursor_theme_load(NULL, 16);
 	if (!theme) {
 		wlr_log(WLR_ERROR, "Failed to load cursor theme");
 		return 1;

examples/pointer.c

@@ -386,7 +386,7 @@ int main(int argc, char *argv[]) {
 		&state.tablet_tool_axis);
 	state.tablet_tool_axis.notify = handle_tablet_tool_axis;
 
-	state.xcursor_manager = wlr_xcursor_manager_create("default", 24);
+	state.xcursor_manager = wlr_xcursor_manager_create(NULL, 24);
 	if (!state.xcursor_manager) {
 		wlr_log(WLR_ERROR, "Failed to load default cursor");
 		return 1;