Remove nullability of local

Author: fitzgen

test/core/gc/array_new_data.wast

@@ -24,7 +24,7 @@
   (data $d "\aa\bb\cc\dd")
 
   (func (export "array-new-data-contents") (result i32 i32)
-    (local (ref null $arr))
+    (local (ref $arr))
     (local.set 0 (array.new_data $arr $d (i32.const 1) (i32.const 2)))
     (array.get_u $arr (local.get 0) (i32.const 0))
     (array.get_u $arr (local.get 0) (i32.const 1))