fix(linux): Reword error if uninstalling non-existent keyboard

This change reworks the output we show if the user tries to
uninstall a non-existing keyboard. This could be trying to uninstall
a shared keyboard when a user keyboard exists and vice versa. This
change rewords the message to include the area (shared/user), so
hopefully this makes it a bit clearer. We also now output this as a
warning instead of an error.

Completely suppressing the message as suggested in #9213 doesn't seem
to be the right way as that would lead to the user blaming uninstall
to not work when the real reason are wrong parameters.

Closes #9213.