Don't rely on system libs in PPA builds

[TheAssassin]

Pre-submit checks

• [X] I checked for similar issues beforehand, but could not find any. I could not add my proposal to any existing issue.
• [X] I am going to take the time to to fill in all the required details. I know that the bug report will be dismissed otherwise.

Feature description

It's annoying to have PPA packages that don't support all the features. We should probably change this.

Proposed solution

We don't want to package libappimage, libappimageupdate separately ourselves. I think that we could just stop trying to use system libraries and build AppImageLauncher the same way we build it here on GitHub. (Not sure if Launchpad will let us check out everything recursively, though.)

Alternative solutions you considered

Package everything separately. We don't want to do that, really.

Additional context

No response