Remove LOGC()

It is not clear when to use LOGC() rather than LOGE(). Always use
LOGE().

Moreover, enum sc_log_level has no "critical" log level.

app/src/controller.c

@@ -113,7 +113,7 @@ sc_controller_start(struct sc_controller *controller) {
     bool ok = sc_thread_create(&controller->thread, run_controller,
                                "scrcpy-ctl", controller);
     if (!ok) {
-        LOGC("Could not start controller thread");
+        LOGE("Could not start controller thread");
         return false;
     }