Due to the switch to Python 3, Toaster master can only build
with master and not with earlier releases.
Make master the default release for projects and remove previous
releases from configuration.
(From OE-Core rev: b96683079fc481080ba7b49731bec697b43edae8)
Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>