Remove "... via Slack" from text created by Slack Integration

The Slack <-> Jira integration works pretty well, it's varey handy to be able to comment on issues directlry from within Slack, but the downside is that the integration adds text to such actions.

For example when commenting via Slack, the text This comment was left via Slack gets appenden to the message. This is unnecessary (I honestly cannot think of any reason why anyone would care about this) and clutters the issues and as such makes this rather annoying.

Please add an option to disable this (or, if this exists already, make it more obvious how to get to this option).