More work on masks (#607)

* Add a #air mask, the opposite of #existing (#1511)

(cherry picked from commit 84fa2bbbc63de7bece01f41c0d5cb7d85cf129e6)

* Remove unused methods in Mask.java

* Remove `test(Extent, BlockVector3)` from Masks.

This was a poorly planned idea. This should save some memory too.

Authored-by: Matthew Miller <mnmiller1@me.com>

worldedit-core/src/main/java/com/boydti/fawe/util/TextureUtil.java

@@ -376,7 +376,7 @@ public class TextureUtil implements TextureHolder {
         for (int typeId : tu.getValidBlockIds()) {
             BlockType block = BlockTypes.get(typeId);
             extent.init(0, 0, 0, block.getDefaultState().toBaseBlock());
-            if (mask.test(extent, extent)) {
+            if (mask.test(extent)) {
                 blocks.add(block);
             }
         }