[Packman] Packages disappear from the list after removing

After removing an installed package via the Package Manager, that package will no longer appear in the Package Manager UI's list of available packages. The editor will need to force an update to Package Manager to make the package reappear (for example by restarting), blocking the user from installing it.

Similar issues were observed in 2019.2 but resolved. This behavior (or similar) seems to be reintroduced in 2019.3.0A11.

Steps to reproduce:
1- Create a new project
2- Using Package Manager, install any package which is not already installed
3- After completed, use Package Manager to remove this package
4- After the package has been removed, observe the entry for that package no longer exists in the list
5- Restart the editor
6- Open Package Manager, observing the entry for that package has reappeared