Revert of Pool implementation for zone segments

src/zone/zone-segment.h

Index: src/zone/zone-segment.h
diff --git a/src/zone/zone-segment.h b/src/zone/zone-segment.h
index 1c85d1148dba94644e86e2c5a5a41bd6b87bd1c5..140112c102bd85864c5683c0053d880a5f03562c 100644
--- a/src/zone/zone-segment.h
+++ b/src/zone/zone-segment.h
@@ -38,17 +38,7 @@
   Address start() const { return address(sizeof(Segment)); }
   Address end() const { return address(size_); }
 
-  // Zap the contents of the segment (but not the header).
-  void ZapContents();
-  // Zaps the header and makes the segment unusable this way.
-  void ZapHeader();
-
  private:
-#ifdef DEBUG
-  // Constant byte value used for zapping dead memory in debug mode.
-  static const unsigned char kZapDeadByte = 0xcd;
-#endif
-
   // Computes the address of the nth byte in this segment.
   Address address(size_t n) const { return Address(this) + n; }