Remove systemd dependency on syslog target

Neither rabbitmq nor any dependent services in chain actually relies on
syslog, so why keep it?

This tested in Fedora since 2016-01. See this commit:

http://pkgs.fedoraproject.org/cgit/rpms/rabbitmq-server.git/commit/?id=1477671

Nobody complained so far.

Signed-off-by: Peter Lemenkov <[email protected]>

Merge pull request rabbitmq#798 from rabbitmq/rabbitmq-server-546

Bump minimal required version to 18.3

(c) year

Merge pull request rabbitmq#773 from rabbitmq/rabbitmq-server-772

Add log information during the network_partition

Merge pull request rabbitmq#773 from rabbitmq/rabbitmq-server-772

Add log information during the network_partition

Merge branch 'stable'

Merge pull request rabbitmq#722 from rabbitmq/rabbitmq-auth-backend-l…

…dap-13

Include vhost to direct connection authentication properties.

Merge pull request rabbitmq#762 from bogdando/bug/1541471

Stop process when rabbit is running but is not connected to master.

Merge pull request rabbitmq#748 from rabbitmq/rabbitmq-server-714

Stop deleted GM member when partial partition is detected

Merge pull request rabbitmq#726 from rabbitmq/rabbitmq-management-166

Update owner of mgmt_db tables