Remove unused osc_plugin environment

This environment is not used and broken, none of the files exist.
Remove it, this is not needed.

Change-Id: Icf053b6104192d8adc883a9cfb9b922ba0089880

tox.ini

@@ -45,20 +45,6 @@ commands =
 [testenv:debug]
 commands = oslo_debug_helper {posargs}
 
-[testenv:osc_plugins]
-deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
-  -r{toxinidir}/requirements.txt
-  ../../x/pbrx
-whitelist_externals =
-  bash
-commands =
-  # bash wrapper is required to handle a subshell of find.
-  bash ./tests/install-siblings.sh
-  pbr freeze
-  openstack --version
-  python tests/check_osc_commands.py
-
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
 # W504 line break after binary operator