Remove the zxJDBC dialect and its entry points

[aminghadersohi]

Problem

ibm_db_sa/zxjdbc.py imports sqlalchemy.connectors.zxJDBC, which SQLAlchemy removed in 1.4. This package declares four sqlalchemy.dialects entry points that point at it:

• db2.zxjdbc, db2.zxjdbc400
• ibm_db_sa.zxjdbc, ibm_db_sa.zxjdbc400

On any supported SQLAlchemy 1.4 or 2.0 install, loading them always raises ModuleNotFoundError: No module named 'sqlalchemy.connectors.zxJDBC'. The dialect also only ever worked on Jython, and Jython cannot install this package (python_requires >= 3.9), so it can't be used even with SQLAlchemy 1.3.

Applications that enumerate installed dialects through entry points, for example to show which databases are available, hit and log this error on every scan.

Change

• Remove ibm_db_sa/zxjdbc.py and its four entry points.
• Remove the two zxjdbc registrations from run_tests.py.
• README: known limitation 7 now mentions PyODBC only.

The ibm_db, pyodbc and AS/400 dialects, and all their entry points, are unchanged.

Verification

Python 3.11, SQLAlchemy 2.0.52. The script loads every sqlalchemy.dialects entry point this distribution declares:

Build	Loaded	Failed
master 7f3866e (0.4.4)	8	4 (all four zxjdbc: No module named 'sqlalchemy.connectors.zxJDBC')
this branch	8	0

The same four failures reproduce with released 0.4.0 on SQLAlchemy 1.4.54. The built wheel's entry_points.txt lists exactly the eight remaining dialects, and the wheel contains no zxjdbc module.

[bchoudhary6415]

Hi @bimalkjha ,

This PR looks correct and ready to merge.

As noted in the SQLAlchemy documentation, support for Jython/zxJDBC was removed upstream because it was no longer functional or supported. Since ibm_db_sa still exposes zxJDBC entry points that depend on removed SQLAlchemy code, removing those dead entry points and the unused dialect implementation is the right change.

Reference from SQLAlchemy:
[platform] [removed] ¶

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.

References: #5094

Please merge this PR.

Thank you!