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
4 files changed