Remove (empty) util plugin

The contents of this plugin have mostly been moved into the api plugin,
or removed entirely.

game/plugin/skills/mining/build.gradle

@@ -10,5 +10,5 @@ plugin {
             "tlf30"
     ]
 
-    dependencies = ["api", "util:lookup"]
+    dependencies = ["api"]
 }

game/plugin/util/lookup/build.gradle

@@ -1,3 +0,0 @@
-plugin {
-    name = "entity_lookup"
-}