feat: remove task - Add git apt repository

[robrap]

This task is failing, so we are trying to remove it.

It was added 8 years ago to get GitHub version 1.7.10 or later. Presumably this is no longer needed.

3 years ago we added updating the cache, which could still potentially be needed, but hopefully not.

The error from GoCD:

TASK [common : Add git apt repository] *****************************************
FAILED - RETRYING: Add git apt repository (10 retries left).
FAILED - RETRYING: Add git apt repository (9 retries left).
FAILED - RETRYING: Add git apt repository (8 retries left).
FAILED - RETRYING: Add git apt repository (7 retries left).
FAILED - RETRYING: Add git apt repository (6 retries left).
FAILED - RETRYING: Add git apt repository (5 retries left).
FAILED - RETRYING: Add git apt repository (4 retries left).
FAILED - RETRYING: Add git apt repository (3 retries left).
FAILED - RETRYING: Add git apt repository (2 retries left).
FAILED - RETRYING: Add git apt repository (1 retries left).
fatal: [10.4.11.55]: FAILED! => {
    "attempts": 10,
    "changed": false
}

MSG:

failed to fetch PPA information, error was: Request failed: <urlopen error _ssl.c:1114: The handshake operation timed out>

---

Make sure that the following steps are done before merging:

• Have a Site Reliability Engineer review the PR if you don't own all of the services impacted.
• If you are adding any new default values that need to be overridden when this change goes live, update internal repos and add an entry to the top of the CHANGELOG.
• Performed the appropriate testing.