Remove the old core reflection implementation

Summary

Remove the old core reflection implementation.

Problem

JEP 416 reimplemented the core reflection implementation with method handles in JDK 18. The -Djdk.reflect.useDirectMethodHandle=false was introduced to enable the old core reflection implementation to mitigate any compatibility issue. There has only been a couple of issues about the exception being thrown for invalid arguments. No other issue reported. It's time to remove the old core reflection implementation.

Solution

Remove the old core reflection implementation.

Specification

The -Djdk.reflect.useDirectMethodHandle=false workaround will stop to work.