virt_tests: remove embedded source files

Remove the virt_tests source code that has been extracted to the
standalone virt-framework repository. The CI workflow now installs
the external package via pip.

The deprecation README is retained to direct users to the new
repository at https://github.com/trgill/virt-framework.

Changes:
- Remove __init__.py, __main__.py, strategy.py, testvm.py, util.py
- Remove virt_tests exclude from setup.cfg (no longer needed)
- Update CONTRIBUTING.md to remove virt_tests reference

Assisted-by: Claude Sonnet 4.5 <noreply@anthropic.com>
Signed-off-by: Todd Gill <tgill@redhat.com>

Author: trgill

CONTRIBUTING.md

@@ -84,8 +84,7 @@ Some examples of common subsystem strings used in the project are:
     as the Sphinx documentation in doc/, and the groff formatted man pages in
     the man/ directory).
   * **tests**: changes to any of the test suites. It is also fine to use the
-    specific suite name if that makes sense ("``virt_tests``",
-    "``container_tests``", etc).
+    specific suite name if that makes sense ("``container_tests``", etc).
   * **dist**: package and distribution metadata: RPM spec file, Python project
     and build metadata etc.
   * **scripts**: patches affecting the demo & helper scripts found in the

setup.cfg

@@ -34,7 +34,6 @@ install_requires =
 [options.packages.find]
 exclude =
     tests*
-    virt_tests*
     container_tests*
 
 [flake8]