X87: [compiler] Remove broken support for undetectable strings.

port b62dbf1e (r30132).

original commit messge:

    Support for undetectable strings was officially dropped in
    https://codereview.chromium.org/916753002, but the compilers
    weren't fixed properly.

BUG=

Review URL: https://codereview.chromium.org/1287173002

Cr-Commit-Position: refs/heads/master@{#30156}

src/full-codegen/x87/full-codegen-x87.cc

@@ -4943,11 +4943,7 @@ void FullCodeGenerator::EmitLiteralCompareTypeof(Expression* expr,
   } else if (String::Equals(check, factory->string_string())) {
     __ JumpIfSmi(eax, if_false);
     __ CmpObjectType(eax, FIRST_NONSTRING_TYPE, edx);
-    __ j(above_equal, if_false);
-    // Check for undetectable objects => false.
-    __ test_b(FieldOperand(edx, Map::kBitFieldOffset),
-              1 << Map::kIsUndetectable);
-    Split(zero, if_true, if_false, fall_through);
+    Split(below, if_true, if_false, fall_through);
   } else if (String::Equals(check, factory->symbol_string())) {
     __ JumpIfSmi(eax, if_false);
     __ CmpObjectType(eax, SYMBOL_TYPE, edx);

src/x87/lithium-codegen-x87.cc

@@ -6108,10 +6108,7 @@ Condition LCodeGen::EmitTypeofIs(LTypeofIsAndBranch* instr, Register input) {
   } else if (String::Equals(type_name, factory()->string_string())) {
     __ JumpIfSmi(input, false_label, false_distance);
     __ CmpObjectType(input, FIRST_NONSTRING_TYPE, input);
-    __ j(above_equal, false_label, false_distance);
-    __ test_b(FieldOperand(input, Map::kBitFieldOffset),
-              1 << Map::kIsUndetectable);
-    final_branch_condition = zero;
+    final_branch_condition = below;
 
   } else if (String::Equals(type_name, factory()->symbol_string())) {
     __ JumpIfSmi(input, false_label, false_distance);