Removed cast to ResettableExtent in for loop.

I have no idea why we were casting it when all objects in the loop were ResettableExtents in the first place.

worldedit-core/src/main/java/com/boydti/fawe/object/extent/RandomTransform.java

@@ -48,10 +48,8 @@ public class RandomTransform extends SelectTransform {
             collection = RandomCollection.of(weights, random);
             extents = new LinkedHashSet<>(weights.keySet());
         }
-        for (AbstractDelegateExtent current : extents) {
-            if (current instanceof ResettableExtent) {
-                ((ResettableExtent) current).setExtent(extent);
-            }
+        for (ResettableExtent current : extents) {
+                current.setExtent(extent);
         }
         return this;
     }