Remove ASGI/WSGI and subinterpreter tests from py_SUITE

- Remove test_subinterp_supported and test_parallel_execution tests
- Remove all test_asgi_* tests (response extraction, caching, etc.)
- Simplify test_memory_stats and test_reload by removing subinterp checks

The removed tests tested functionality that was removed in the
ASGI/WSGI runner removal commit.

Author: benoitc