backend: remove get_presentation_clock from interface

Since 1367a4a, only CLOCK_MONOTONIC is
supported.

backend/backend.c

@@ -153,13 +153,6 @@ static struct wlr_session *session_create_and_wait(struct wl_display *disp) {
 	return session;
 }
 
-clockid_t wlr_backend_get_presentation_clock(struct wlr_backend *backend) {
-	if (backend->impl->get_presentation_clock) {
-		return backend->impl->get_presentation_clock(backend);
-	}
-	return CLOCK_MONOTONIC;
-}
-
 int wlr_backend_get_drm_fd(struct wlr_backend *backend) {
 	if (!backend->impl->get_drm_fd) {
 		return -1;

backend/multi/backend.c

@@ -82,20 +82,6 @@ static struct wlr_session *multi_backend_get_session(
 	return backend->session;
 }
 
-static clockid_t multi_backend_get_presentation_clock(
-		struct wlr_backend *backend) {
-	struct wlr_multi_backend *multi = multi_backend_from_backend(backend);
-
-	struct subbackend_state *sub;
-	wl_list_for_each(sub, &multi->backends, link) {
-		if (sub->backend->impl->get_presentation_clock) {
-			return wlr_backend_get_presentation_clock(sub->backend);
-		}
-	}
-
-	return CLOCK_MONOTONIC;
-}
-
 static int multi_backend_get_drm_fd(struct wlr_backend *backend) {
 	struct wlr_multi_backend *multi = multi_backend_from_backend(backend);
 
@@ -114,7 +100,6 @@ static const struct wlr_backend_impl backend_impl = {
 	.destroy = multi_backend_destroy,
 	.get_renderer = multi_backend_get_renderer,
 	.get_session = multi_backend_get_session,
-	.get_presentation_clock = multi_backend_get_presentation_clock,
 	.get_drm_fd = multi_backend_get_drm_fd,
 };
 

include/wlr/backend/interface.h

@@ -18,7 +18,6 @@ struct wlr_backend_impl {
 	void (*destroy)(struct wlr_backend *backend);
 	struct wlr_renderer *(*get_renderer)(struct wlr_backend *backend);
 	struct wlr_session *(*get_session)(struct wlr_backend *backend);
-	clockid_t (*get_presentation_clock)(struct wlr_backend *backend);
 	int (*get_drm_fd)(struct wlr_backend *backend);
 	uint32_t (*get_buffer_caps)(struct wlr_backend *backend);
 };