Revert "selftests/ftrace: check for do_sys_openat2 in user-memory test"

This reverts commit 9110e2f2.

This commit is not suitable for 5.4-stable because the openat2 system
call does not exist in v5.4.

Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>