api: remove tileitem spawn time

This was never used and has limited use

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

@@ -36,10 +36,4 @@ public interface TileItem extends Renderable
 	int getId();
 
 	int getQuantity();
-
-	/**
-	 * Time in game ticks when the item spawned (relative to us)
-	 * @return
-	 */
-	int getSpawnTime();
 }