Remove logfile & email functionality

[rohanpm]

alt-src has a few features relating to logging which are not useful to us currently, since the tool is integrated with Pub which has its own logging.

We should drop logfile functionality because:

• The cause of errors, rather than being captured in Pub logs, ends up captured in a separate log file which is only accessible by superusers
• The log files are stored in working directories which can be deleted in many circumstances, ultimately resulting in any info which only went to the log file being lost
• It may be interfering with capturing the output from some subcommands (a little unclear, as current code looks like it should work, but we saw sometimes the output of rsync did not end up in either stdout/stderr or in the log file).

We should similarly drop email functionality because:

• nobody reads/reacts to the emails - in practice we don't even send them to the right person
• we have better methods of alerting; it's possible to trigger Splunk alerts from Pub logs, for instance.

These two are combined into one issue because logging/email functionality seems to be a little intertwined.

Acceptance criteria

• alt-src no longer creates separate log files, and related code no longer exists.
• Any output which formerly went to log files now instead goes to the loggers within the alt-src process, or stdout, or stderr.
  -- (An exception could be made if some of this output is determined to be unreasonably verbose.)
• alt-src no longer attempts to send emails, and related code no longer exists.