Add an uninstall rule

**Is your feature request related to a problem? Please describe.**
After building and installing from GitHub source code on Linux, it would be convenient if there was an uninstall rule.

**Describe the solution you'd like**
`$ sudo make uninstall`
to uninstall Audacity.

**Describe alternatives you've considered**
* Manually deleting installed files
* Using Checkinstall

**Additional context**
https://forum.audacityteam.org/viewtopic.php?p=433831#p433831

Start by locating the Linux build/install entry point and the existing install rules or make targets. Confirm which files are installed, then verify that `sudo make uninstall` removes those files without affecting unrelated data.

Written by the indexing model from the issue text.