sargo/yggdrasil: Droidian related fixes/additions

[erikinkinen]

This pull request contains the following updates:

• Updated Droidian download URL on sargo. Pixel 3a has re-gained status as an official port and the official download URL should be used.
• Updated the broke Droidian install directives for yggdrasil. The configuration to install Droidian on Volla Phone has been broken for a while. This fixes it and switches to fastboot installable images which are the preferred way to install as of now.
• Also, add Cutie variant for both sargo and yggdrasil. This downloads from CutieShell CI and also has an appropriate notice displayed to user about the status of Cutie.

[erikinkinen]

Fixed checks by removing unused user_actions from yggdrasil.yml.

Should be good now.

[NotKit]

Looks good to me. Thank you!