net-im/py-slackclient: Update version 2.1.0=>2.9.3

• Mark DEPRECATED as upstream hasstalled develeopment in lieu of slack-client which is in the ports tree now
• Set EXPIRATION_DATE to 2022-06-30
• Disable test as GH repo is no longer available and PyPi sdist do not contain tests

Relnotes: https://pypi.org/project/slackclient/2.9.3/#history