RFR: JDK-8241631 PropertyGetterTaglet, PropertySetterTaglet may be removed

[Jonathan Gibbons]

Please review a very simple change to remove some obsolete classes (two 
taglet classes and a common supertype) from an earlier version of the 
support for JavaFX properties.

The tags were part of an early mechanism to associate getter and setter 
methods with properties.  The association is now done automagically with 
reflection. The only remaining use of these taglets in the standard 
doclet was to just register them for use, and analysis of the JavaFX 
repo confirms that the tags are no longer used in that source base.  The 
tags are not documented in the standard docs[SPEC] and so there is no 
need for any CSR approval to remove them.

There a few references remaining in tests which need to be cleaned up.

No tests because this is just removing obsolete code. [noreg-cleanup]

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8241631
Webrev: http://cr.openjdk.java.net/~jjg/8241631/webrev.00/
SPEC : https://docs.oracle.com/javase/10/docs/specs/doc-comment-spec.html