Remove syslog logger code from CTA

Situation

Recently, all CTA services have been modified to print their logs to a local file instead of rsyslog. We don't plan to go back to rsyslog due to the unnecessary complexity and CPU load that it requires.

Therefore, we can safely remove the rsyslog related code from CTA.

Related issues:

• https://gitlab.cern.ch/cta/operations/-/issues/648
• #488 (closed)
• https://gitlab.cern.ch/cta/operations/-/issues/1254 (rsyslog no longer used after these changes)

Objective

Remove the syslog related code from CTA, in particular the following files:

• common/log/SyslogLogger.cpp
• common/log/SyslogLogger.hpp