Revert of [builtins] Introduce proper Float64Exp operator.

src/compiler/mips64/code-generator-mips64.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/scopes.h"
 #include "src/compiler/code-generator.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/osr.h"
@@ skipping 738 matching lines @@
       __ Daddu(i.OutputRegister(), offset.from_stack_pointer() ? sp : fp,
                Operand(offset.offset()));
       break;
     }
     case kIeee754Float64Atan:
       ASSEMBLE_IEEE754_UNOP(atan);
       break;
     case kIeee754Float64Atan2:
       ASSEMBLE_IEEE754_BINOP(atan2);
       break;
-    case kIeee754Float64Exp:
-      ASSEMBLE_IEEE754_UNOP(exp);
-      break;
     case kIeee754Float64Log:
       ASSEMBLE_IEEE754_UNOP(log);
       break;
     case kIeee754Float64Log1p:
       ASSEMBLE_IEEE754_UNOP(log1p);
       break;
     case kIeee754Float64Log2:
       ASSEMBLE_IEEE754_UNOP(log2);
       break;
     case kIeee754Float64Log10:
@@ skipping 1531 matching lines @@
       padding_size -= v8::internal::Assembler::kInstrSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8