zsh: remove Vincent Bernat from reviewers for ZSH completion

Signed-off-by: Vincent Bernat <vincent@bernat.im>

contrib/completion/zsh/REVIEWERS

@@ -1,3 +1,2 @@
 Tianon Gravi <admwiggin@gmail.com> (@tianon)
 Jessie Frazelle <jess@docker.com> (@jfrazelle)
-Vincent Bernat <vincent@bernat.im> (@vincentbernat)