Revert "Merge pull request #4568 from deathbeam/proper-shutdown"

This reverts commit 8d53997685, reversing
changes made to 4f548e835c.

This is crashing on shutdown.

runelite-api/src/main/java/net/runelite/api/GameEngine.java

@@ -51,9 +51,4 @@ public interface GameEngine
 	 * @return true if on the main thread, false otherwise
 	 */
 	boolean isClientThread();
-
-	/**
-	 * Shut downs all open connections and files in client and serializes not serialized data.
-	 */
-	void shutDown();
 }