Drop Jira proxy settings columns

Description

We no longer need the Jira proxy settings columns in jira_tracker_data table as we are using the proxy settings via environment variables. https://docs.gitlab.com/omnibus/settings/environment-variables.html#setting-custom-environment-variables.

This reverts !52119 (merged).

There is a summary of the reasons to remove the columns #216912 (comment 532238198).

Iterations

Removing columns requires 3 milestones https://docs.gitlab.com/ee/development/what_requires_downtime.html#dropping-columns

• Ignoring the column %13.11 !57260 (merged)
• Dropping the column %13.12 !60123 (merged)
• Removing the ignore rule %14.0 !62218 (merged)