EL-1238 Part C: switch off maintenace mode

[willc-work]

Jira ticket

What changed and why

Turn off maintenance mode and revert circleci config

Guidance to review

This is the 3rd PR and should not be merged until Part B has been merged with main and has fully deployed

Checklist

Before you ask people to review this PR:

• Tests and rubocop should be passing
• Branch is generally up to date with main Github - definitely no conflicts
• No unnecessary whitespace changes. These make diffs harder to read and conflicts more likely.
• PR description says what changed and why, with a link to the JIRA story.
• Diff has been checked for unexpected changes being included.
• Commit messages say why the change was made.