maint: remove redundant Travis CI notifications.
maint: remove redundant Travis CI notifications.

* .travis.yml (env.global): Didn't work here, so move back to
env key.
(notifications): Remove.  Default is to do the same thing anyway.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

GUI/lyaml,GUI/lyaml