[compiler] Remove broken support for undetectable strings.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 9824a5c0c05a5465e07140557a59f7190b6250ad..6504fc168faaa93da933a55471059d8c271a5d3f 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -5652,10 +5652,7 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
   } else if (String::Equals(type_name, factory->string_string())) {
     __ JumpIfSmi(input, false_label);
     __ CompareObjectType(input, scratch, no_reg, FIRST_NONSTRING_TYPE);
-    __ b(ge, false_label);
-    __ ldrb(scratch, FieldMemOperand(scratch, Map::kBitFieldOffset));
-    __ tst(scratch, Operand(1 << Map::kIsUndetectable));
-    final_branch_condition = eq;
+    final_branch_condition = lt;
 
   } else if (String::Equals(type_name, factory->symbol_string())) {
     __ JumpIfSmi(input, false_label);