selftests: lib: remove strscpy test

The strscpy test loads test_strscpy module for testing. But test_strscpy
was converted to Kunit (see fixes). Hence remove strscpy.

Fixes: 41eefc46 ("string: Convert strscpy() self-test to KUnit")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>