Remove standard-test-rhts role.
standard-test-rhts had next defects:
* The role used only dnf.
* It didn't work with Atomic Host.
* It installed beakerlib-libraries, which was very confusing.
* It used restrain framework as suit to run tests.
All this were confusing. beakerlib-libraries now supported by
standard-test-beakerlib role.
Signed-off-by: Andrei Stepanov <astepano@redhat.com>