[ticket/12147] Remove Travis CI notifications.

We don't want to get notifications for branches other people are working on.

PHPBB3-12147
Merge remote-tracking branch 'github-bantu/ticket/12147' into develop-olympus

* github-bantu/ticket/12147:
  [ticket/12147] Remove Travis CI notifications.
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/12147] Remove Travis CI notifications.

Conflicts:
	.travis.yml