Get rid of duplicated CPU::DebugBreak() method.

src/arm/cpu-arm.cc

Index: src/arm/cpu-arm.cc
diff --git a/src/arm/cpu-arm.cc b/src/arm/cpu-arm.cc
index 8766a24bb2adc6d86e9247920bda1fde30cb84b8..cf531e1292bd8e4e7c1fa2e3e551b5167354a78f 100644
--- a/src/arm/cpu-arm.cc
+++ b/src/arm/cpu-arm.cc
@@ -106,15 +106,6 @@ void CPU::FlushICache(void* start, size_t size) {
 #endif
 }
 
-
-void CPU::DebugBreak() {
-#if !defined (__arm__)
-  UNIMPLEMENTED();  // when building ARM emulator target
-#else
-  asm volatile("bkpt 0");
-#endif
-}
-
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM