Remove CheckNotRegistersEqual regexp-masm function from all architectures.

src/mips/regexp-macro-assembler-mips.cc

Index: src/mips/regexp-macro-assembler-mips.cc
diff --git a/src/mips/regexp-macro-assembler-mips.cc b/src/mips/regexp-macro-assembler-mips.cc
index 0d8ae972b46ce30c6c2d93e22c707aeb788e6415..4f242cabbb6ca50f88f3ca00ad1683d26d0a076e 100644
--- a/src/mips/regexp-macro-assembler-mips.cc
+++ b/src/mips/regexp-macro-assembler-mips.cc
@@ -444,13 +444,6 @@ void RegExpMacroAssemblerMIPS::CheckNotBackReference(
 }
 
 
-void RegExpMacroAssemblerMIPS::CheckNotRegistersEqual(int reg1,
-                                                      int reg2,
-                                                      Label* on_not_equal) {
-  UNIMPLEMENTED_MIPS();
-}
-
-
 void RegExpMacroAssemblerMIPS::CheckNotCharacter(uint32_t c,
                                                 Label* on_not_equal) {
   BranchOrBacktrack(on_not_equal, ne, current_character(), Operand(c));