Remove jython code, remove all jython / pypy symbols

Remove jython code, remove all jython / pypy symbols

Removed all dialect code related to support for Jython and zxJDBC. Jython
has not been supported by SQLAlchemy for many years and it is not expected
that the current zxJDBC code is at all functional; for the moment it just
takes up space and adds confusion by showing up in documentation. At the
moment, it appears that Jython has achieved Python 2.7 support in its
releases but not Python 3.   If Jython were to be supported again, the form
it should take is against the Python 3 version of Jython, and the various
zxJDBC stubs for various backends should be implemented as a third party
dialect.

Additionally modernized logic that distinguishes between "cpython"
and "pypy" to instead look at platform.python_distribution() which
reliably tells us if we are cPython or not; all booleans which
previously checked for pypy and sometimes jython are now converted
to be "not cpython", this impacts the test suite for tests that are
cPython centric.

Fixes: #5094
Change-Id: I226cb55827f997daf6b4f4a755c18e7f4eb8d9ad