testsuite: Improve fake_delete behavior

testsuite: Improve fake_delete behavior

- When fake delete_module() succeeds, remove its entry from /sys/module.
- Add tests to ensure module is properly removed.

Co-developed-by: Qingqing Li <qingqing.li@intel.com>
Signed-off-by: Qingqing Li <qingqing.li@intel.com>
Signed-off-by: Dan He <dan.h.he@intel.com>
Signed-off-by: Gongjun Song <gongjun.song@intel.com>
Signed-off-by: Yuchi Chen <yuchi.chen@intel.com>
Signed-off-by: Wenjie Wang <wenjie2.wang@intel.com>
Link: https://github.com/kmod-project/kmod/pull/309
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>