Hello!

This patch adds an interactive command 'project-remove-known-project',
that lets the user interactively remove a project from the project
list.  My usecase is that sometimes when a directory is moved, the
project isn't deleted from the list.

This command is modelled after the already present
'project--remove-from-project-list', but that function isn't
interactive, and also has a specific purpose.

I did not add a binding, nor add it to the
project-switch-commands. Unsure if deserves a spot there :).

--
Theodor Thornhill