[interpreter] Drop overprotective --harmony-instanceof check.

The check in question will trigger because one of our unit tests still
emits the bytecode (i.e. unittests/BytecodeArrayBuilderTest) even when
the flag is turned on by default.

R=rmcilroy@chromium.org
TEST=unittests/BytecodeArrayBuilderTest.AllBytecodesGenerated

Review URL: https://codereview.chromium.org/1820753003

Cr-Commit-Position: refs/heads/master@{#34954}

src/interpreter/bytecode-array-builder.cc

@@ -1433,7 +1433,6 @@ Bytecode BytecodeArrayBuilder::BytecodeForCompareOperation(Token::Value op) {
     case Token::Value::GTE:
       return Bytecode::kTestGreaterThanOrEqual;
     case Token::Value::INSTANCEOF:
-      DCHECK(!FLAG_harmony_instanceof);
       return Bytecode::kTestInstanceOf;
     case Token::Value::IN:
       return Bytecode::kTestIn;