Clean up remainders of USE_SYSTEMD and logging setup

We dropped the ability to override USE_SYSTEMD to False when we deleted
screen support in [0], so we can also clean up any conditionals based
on it.

Also clean up the logging setup functions, dropping local vars for
parameters that we don't actually support anymore.

[0] I8c27182f60b0f5310b3a8bf5feb02beb7ffbb26a

Change-Id: I5cbce9f2c42e111761e8689447b3f8cbb7ea2eb5
diff --git a/stack.sh b/stack.sh
index 089510f..f00bceb 100755
--- a/stack.sh
+++ b/stack.sh
@@ -803,13 +803,11 @@
 # Install subunit for the subunit output stream
 pip_install -U os-testr
 
-if [[ "$USE_SYSTEMD" == "True" ]]; then
-    pip_install_gr systemd-python
-    # the default rate limit of 1000 messages / 30 seconds is not
-    # sufficient given how verbose our logging is.
-    iniset -sudo /etc/systemd/journald.conf "Journal" "RateLimitBurst" "0"
-    sudo systemctl restart systemd-journald
-fi
+pip_install_gr systemd-python
+# the default rate limit of 1000 messages / 30 seconds is not
+# sufficient given how verbose our logging is.
+iniset -sudo /etc/systemd/journald.conf "Journal" "RateLimitBurst" "0"
+sudo systemctl restart systemd-journald
 
 # Virtual Environment
 # -------------------
@@ -1521,14 +1519,11 @@
     echo
 fi
 
-# If USE_SYSTEMD is enabled, tell the user about using it.
-if [[ "$USE_SYSTEMD" == "True" ]]; then
-    echo
-    echo "Services are running under systemd unit files."
-    echo "For more information see: "
-    echo "https://docs.openstack.org/devstack/latest/systemd.html"
-    echo
-fi
+echo
+echo "Services are running under systemd unit files."
+echo "For more information see: "
+echo "https://docs.openstack.org/devstack/latest/systemd.html"
+echo
 
 # Useful info on current state
 cat /etc/devstack-version