www/py-meld3: Update to 2.0.1 and DEPRECATE

The meld3 package should be considered unmaintained as of April 2020.
See https://pypi.org/project/meld3/

This is a leaf port.

PR: 249217
Submitted by: gspurki@gmail.com
Approved by: tn@0x746e.org.ua (maintainer timeout > 1 month)