Remove reference to PPAs

They have not been maintained in a while, therefore we are deprecating this installation option. They have been third-party anyway.

Author: TheAssassin

README.md

@@ -134,11 +134,6 @@ Compatibility table (likely incomplete.) Please, feel free to open PRs to add di
 
 The installation of packages on systems with a set of packages similar to one of the listed ones (e.g., Linux Mint, Fedora, etc.) should work as well.
 
-**Note:** For Ubuntu 19.04 and newer as well as derivatives, there's two PPAs (personal package archives) available providing a simple way to install and update AppImageLauncher (thanks [Peter Jonas](https://github.com/shoogle) for creating and maintaining them):
-
-  - stable (provides all releases): https://launchpad.net/~appimagelauncher-team/+archive/ubuntu/stable
-  - daily (latest and greatest but possibly unstable): https://launchpad.net/~appimagelauncher-team/+archive/ubuntu/daily
-
 Manjaro and Netrunner Rolling users can install AppImageLauncher with a distribution-provided package called `appimagelauncher`.
 
 Arch Linux, Manjaro, Antergos and Netrunner Rolling users can use AUR to install AppImageLauncher by installing [appimagelauncher](https://aur.archlinux.org/packages/appimagelauncher) or [appimagelauncher-git](https://aur.archlinux.org/packages/appimagelauncher-git) (possibly broken, see [#574](https://github.com/TheAssassin/AppImageLauncher/issues/574)) (thanks @NuLogicSystems for setting up the build).