8205132: Remove Thread.countStackFrames()

Thread::countStackFrames has been deprecated for 20+ years and has been marked for-removal since Java SE 9. I'd like to remove it for Java SE 14. It's was never a well-defined method and I've been unable to find anything that uses it. The StackWalker API is a much better solution for code that is interested in the number of stack frames. The changes to remove this method are here: http://cr.openjdk.java.net/~alanb/8205132/webrev/ The CSR will need a Reviewer: https://bugs.openjdk.java.net/browse/JDK-8232654 -Alan