[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index e767ee3261b99bbf5add477afef23cefee9de4aa..a7759c32e16a6300a5501174593c6330d9a3e89a 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -117,9 +117,6 @@ struct Register {
     Register r = {code};
     return r;
   }
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool is_valid() const { return 0 <= reg_code && reg_code < kNumRegisters; }
   bool is(Register reg) const { return reg_code == reg.reg_code; }
   int code() const {
@@ -221,9 +218,6 @@ struct XMMRegister {
     return result;
   }
 
-  const char* ToString();
-  bool IsAllocatable(RegisterConfiguration::CompilerSelector compiler =
-                         RegisterConfiguration::CRANKSHAFT) const;
   bool is_valid() const { return 0 <= reg_code && reg_code < kMaxNumRegisters; }
   bool is(XMMRegister reg) const { return reg_code == reg.reg_code; }
   int code() const {