[MISC] 8.4 - Cleanup K8s legacy permissions fix

[sinclert-canonical]

This PR removes an old MySQL data directory permissions fix, reverting this old PR.

As far as I understand, we are already setting the permissions in the charmed MySQL rock (see code), but the /var/lib/mysql folder does not exist yet. To that end, I am proposing to explicitly create such folder before the ownership change takes place (see PR). This will need to be updated, pointing at the new image SHA.

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Required for MySQL K8s charm in root-less mode.

[astrojuanlu]

I'm confused. The changes in the MySQL rock predate canonical/mysql-k8s-operator#238 by a few months 🤔

[sinclert-canonical]

I'm confused. The changes in the MySQL rock predate canonical/mysql-k8s-operator#238 by a few months

Yes, let me figure out why. Worst case, we make changes to the charmed rock first, then bump the rock SHA-256 to point at the upcoming rock, alongside this cleanup.

[sinclert-canonical]

I'm confused. The changes in the MySQL rock predate canonical/mysql-k8s-operator#238 by a few months

Spent a bit of time figuring out what was wrong:

In fact, the bug described in the removed function doc-string is still there: when initializing the MySQL data directory within the charm, the /var/lib/mysql folder belongs to root, while doing so directly into the rock (by locally building it, copying it to Docker, and SSH-ing into a runner container), makes it belong to mysql.

Therefore, in order to prevent a regression in the charm behavior when initializing the MySQL data directory, such directory needs to be created + changed ownership in the rock. I tested this approach in this PR, and apparently MySQL can initialize the data directory, even if it already exists, as long as it is completely empty.

I will update the PR description accordingly.