Replace the use CharacterStreams in Heap::AllocateSymbolInternal and String::ComputeHash

src/unicode.h

Index: src/unicode.h
diff --git a/src/unicode.h b/src/unicode.h
index 91b16c9f3564f4f0fbb0846381ef02028b773f12..f2f257dd7d4346e7a58e28280ef2f68d63e85d44 100644
--- a/src/unicode.h
+++ b/src/unicode.h
@@ -170,10 +170,6 @@ class Utf8 {
   // that match are coded as a 4 byte UTF-8 sequence.
   static const unsigned kBytesSavedByCombiningSurrogates = 2;
   static const unsigned kSizeOfUnmatchedSurrogate = 3;
-
- private:
-  template <unsigned s> friend class Utf8InputBuffer;
-  friend class Test;
   static inline uchar ValueOf(const byte* str,
                               unsigned length,
                               unsigned* cursor);