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.