Maintenance: Fix unused and undefined variable analysis warnings

Building off of #1760

Remove the following from `phpcs.xml.dist` and then fix the new issues when running `phpcs`.
```xml
4
```
from:
```xml

includes/admin/views/
templates/

4

```

Some of these variables go into templates. It might be worth taking this opportunity to document variable usage in the templates.

Start in phpcs.xml.dist and remove the severity setting from the VariableAnalysis rule. Run phpcs to identify the newly reported issues, including those in includes/admin/views/ and templates, then inspect each warning and fix the affected variables. Done means the analysis passes without those exclusions; document template variable usage if needed.

Written by the indexing model from the issue text.