8237882: ZGC: Remove ZUtils::round_{up,down}_power_of_2() declarations

Reviewed-by: kbarrett, smonteith

src/hotspot/share/gc/z/zUtils.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -31,10 +31,6 @@ class ZUtils : public AllStatic {
   // Allocation
   static uintptr_t alloc_aligned(size_t alignment, size_t size);
 
-  // Power of two
-  static size_t round_up_power_of_2(size_t value);
-  static size_t round_down_power_of_2(size_t value);
-
   // Size conversion
   static size_t bytes_to_words(size_t size_in_words);
   static size_t words_to_bytes(size_t size_in_words);