Don't install python3-eventlet for worker

It was there so that we could switch between gevent & eventlet
for a greenlets library (for concurrency pool), but never actually tried it.
We've been using gevent for several months now.

files/install-deps-worker.yaml

@@ -36,9 +36,7 @@
           - postgresql # pg_dump
           - python3-boto3 # AWS (S3)
           - python3-fasjson-client
-          # remove if we decide not to use concurrency
-          - python3-eventlet
-          - python3-gevent
+          - python3-gevent # concurrency pool, see run_worker.sh
           # v6 = bodhi-client, v5 = python3-bodhi{,-client}
           - bodhi-client
         # needed when installing from koji - there are no GPG-signed packages

files/run_worker.sh

@@ -38,7 +38,7 @@ elif [[ "${CELERY_COMMAND}" == "worker" ]]; then
     CONCURRENCY="${CONCURRENCY:-$DEFAULT_CONCURRENCY}"
     export CONCURRENCY
 
-    # Options: prefork | eventlet | gevent | solo
+    # Options: solo | gevent
     # https://www.distributedpython.com/2018/10/26/celery-execution-pool/
     DEFAULT_POOL="solo"
     DEFAULT_CONCURRENCY_POOL="gevent"