[assembler] Remove dead no_reg definitions

We have the generic {no_reg} and {no_dreg}, other definitions are dead.
Currently even {no_dreg} is dead, but I am keeping this because I can
see future need for that.

R=mstarzinger@chromium.org

Bug: v8:8238
Change-Id: I0de597fead6b3def18fd5c530419d3c149f235a8
Reviewed-on: https://chromium-review.googlesource.com/1251123Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56288}

src/ia32/assembler-ia32.h

@@ -140,7 +140,6 @@ typedef XMMRegister Simd128Register;
   constexpr DoubleRegister R = DoubleRegister::from_code<kDoubleCode_##R>();
 DOUBLE_REGISTERS(DEFINE_REGISTER)
 #undef DEFINE_REGISTER
-constexpr DoubleRegister no_double_reg = DoubleRegister::no_reg();
 constexpr DoubleRegister no_dreg = DoubleRegister::no_reg();
 
 // Note that the bit values must match those used in actual instruction encoding

src/mips/assembler-mips.h

@@ -304,7 +304,6 @@ typedef FPURegister DoubleRegister;
 DOUBLE_REGISTERS(DECLARE_DOUBLE_REGISTER)
 #undef DECLARE_DOUBLE_REGISTER
 
-constexpr DoubleRegister no_freg = DoubleRegister::no_reg();
 constexpr DoubleRegister no_dreg = DoubleRegister::no_reg();
 
 // SIMD registers.

src/mips64/assembler-mips64.h

@@ -309,7 +309,6 @@ typedef FPURegister DoubleRegister;
 DOUBLE_REGISTERS(DECLARE_DOUBLE_REGISTER)
 #undef DECLARE_DOUBLE_REGISTER
 
-constexpr DoubleRegister no_freg = DoubleRegister::no_reg();
 constexpr DoubleRegister no_dreg = DoubleRegister::no_reg();
 
 // SIMD registers.

src/x64/assembler-x64.h

@@ -219,7 +219,6 @@ typedef XMMRegister Simd128Register;
   constexpr DoubleRegister R = DoubleRegister::from_code<kDoubleCode_##R>();
 DOUBLE_REGISTERS(DECLARE_REGISTER)
 #undef DECLARE_REGISTER
-constexpr DoubleRegister no_double_reg = DoubleRegister::no_reg();
 constexpr DoubleRegister no_dreg = DoubleRegister::no_reg();
 
 enum Condition {