Remove suggestion to @ the maintainers

We're subscribed to the repo already so there's no need.

Author: Daniel Magliola

CONTRIBUTING.md

@@ -2,9 +2,7 @@
 
 Prometheus uses GitHub to manage reviews of pull requests.
 
-* If you have a trivial fix or improvement, go ahead and create a pull request,
-  addressing (with `@...`) the maintainer of this repository (see
-  [MAINTAINERS.md](MAINTAINERS.md)) in the description of the pull request.
+* If you have a trivial fix or improvement, go ahead and create a pull request.
 
 * If you plan to do something more involved, first discuss your ideas
   on our [mailing list](https://groups.google.com/forum/?fromgroups#!forum/prometheus-developers).