[arm64] Bug fix in sapefoint recording.

cp is handled by the register allocator and doesn't necessarily hold the
context pointer on arm64.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/695323005

Cr-Commit-Position: refs/heads/master@{#25209}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25209 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm64/lithium-codegen-arm64.cc

@@ -557,11 +557,6 @@ void LCodeGen::RecordSafepoint(LPointerMap* pointers,
       safepoint.DefinePointerRegister(ToRegister(pointer), zone());
     }
   }
-
-  if (kind & Safepoint::kWithRegisters) {
-    // Register cp always contains a pointer to the context.
-    safepoint.DefinePointerRegister(cp, zone());
-  }
 }
 
 void LCodeGen::RecordSafepoint(LPointerMap* pointers,