UI: Fix unorthodox macOS Dock icon behavior

Fixes overriding of macOS dock icon behavior.

macOS sets the icon on launch based on:
- The Information PLIST
- A user provided icon by Finder

setWindowIcon overrides this behavior.

Therefore, this commit resolves this issue,
by doing nothing if target is macOS.

UI/obs-app.cpp

@@ -1164,10 +1164,7 @@ OBSApp::OBSApp(int &argc, char **argv, profiler_name_store_t *store)
 
 	sleepInhibitor = os_inhibit_sleep_create("OBS Video/audio");
 
-#ifdef __APPLE__
-	setWindowIcon(
-		QIcon::fromTheme("obs", QIcon(":/res/images/obs_256x256.png")));
-#else
+#ifndef __APPLE__
 	setWindowIcon(QIcon::fromTheme("obs", QIcon(":/res/images/obs.png")));
 #endif