fix(kill_stress_thread): remove scylla-bench/gemini kills
fix(kill_stress_thread): remove scylla-bench/gemini kills

now the scylla-bench and gemini are running inside docker
we don't need to kill them directly, there's a docker kill
command that should stop them.

Fixes: #5264

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests