Michael Baudino authored Apr 19, 2019 and OyyoDams committed May 07, 2019

This commit removes the Buildroot package for the legacy web manager. It
is not used on any board anymore.

It also adds a migration to bump webmanager from 1 to 2 in users
existing `recalbox.conf`.

Finally, it adds a warning in the logs when a user somehow manages to
try to start webmanager v1.

Signed-off-by: Michael Baudino <michael.baudino@alpine-lab.com>