Remove NearestNextGapPos. It is not used anymore.

src/x64/lithium-x64.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 198 matching lines @@
   bool IsGapAt(int index) const {
     UNIMPLEMENTED();
     return false;
   }
 
   int NearestGapPos(int index) const {
     UNIMPLEMENTED();
     return 0;
   }
 
-  int NearestNextGapPos(int index) const {
-    UNIMPLEMENTED();
-    return 0;
-  }
-
   void MarkEmptyBlocks() { UNIMPLEMENTED(); }
 
 #ifdef DEBUG
   void Verify() { UNIMPLEMENTED(); }
 #endif
 };
 
 
 class LChunkBuilder BASE_EMBEDDED {
  public:
@@ skipping 13 matching lines @@
   HYDROGEN_CONCRETE_INSTRUCTION_LIST(DECLARE_DO)
 #undef DECLARE_DO
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_LITHIUM_X64_H_