contrib: remove REVIEWERS files

We were not really using these, and they haven't been
updated in a long time. If needed, we can add people to
the CODEOWNERS file.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

contrib/REVIEWERS

@@ -1 +0,0 @@
-Tianon Gravi <admwiggin@gmail.com> (@tianon)

contrib/init/systemd/REVIEWERS

@@ -1,3 +0,0 @@
-Lokesh Mandvekar <lsm5@fedoraproject.org> (@lsm5)
-Brandon Philips <brandon.philips@coreos.com> (@philips)
-Jessie Frazelle <jess@docker.com> (@jfrazelle)

contrib/init/upstart/REVIEWERS

@@ -1,2 +0,0 @@
-Tianon Gravi <admwiggin@gmail.com> (@tianon)
-Jessie Frazelle <jess@docker.com> (@jfrazelle)