[php-src] PR #24312: ext/session: simplify temp directory handling in tests

Pull Request: https://github.com/php/php-src/pull/24312 Author: jorgsowa Cleanup of CLEAN section in ext/session - bug42596.phpt: dropped the rmdir() before mkdir(), and moved the file and directory cleanup into a --CLEAN-- section. - bug61470.phpt: uses its own bug61470 directory as the save path instead of the tests directory, so it no longer writes session files there. The sess_* cleanup and rmdir() are in --CLEAN--. - rfc1867_sid_invalid.phpt: removed the --CLEAN-- section, which deleted a file nothing creates. - session_save_path_variation4.phpt: dropped the rmdir() before mkdir(), and --CLEAN-- is now a single rmdir(). - session_save_path_variation5.phpt: same changes as session_save_path_variation4.phpt.