RFR: 2244: SecurityLevel in JiraHost is useless [v3]

[Zhao Song]

> SecurityLevel in JiraHost is rarely used and sometimes it will conflict with the security configuration of issueNotifier. So there is no point to keep it. Also, I removed the support of `/issue create` command in this patch as ErikJ suggested. 
> 
> There is one useful usage of `securityLevel`, it's in `JiraIssue#addWebLink`, skara bot uses the security to determine if the link should be posted as a comment. But I think it can be replaced by checking the visibilityRole of the jiraHost.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  update

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1642/files
  - new: https://git.openjdk.org/skara/pull/1642/files/7ba90afa..ece8d34e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1642&range=02
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1642&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1642.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1642/head:pull/1642

PR: https://git.openjdk.org/skara/pull/1642