Merge branch 'cleanup-readme' into 'master'

Remove Coveralls and Semaphore badges. [ci skip]

Remove Coveralls and Semaphore badges from the README. They're outdated,
unused, and not GitLab CI :)

[ci skip]

See merge request !4334

README.md

 # GitLab
 
 [![build status](https://gitlab.com/gitlab-org/gitlab-ce/badges/master/build.svg)](https://gitlab.com/gitlab-org/gitlab-ce/commits/master)
-[![Build Status](https://semaphoreci.com/api/v1/projects/2f1a5809-418b-4cc2-a1f4-819607579fe7/400484/shields_badge.svg)](https://semaphoreci.com/gitlabhq/gitlabhq)
 [![Code Climate](https://codeclimate.com/github/gitlabhq/gitlabhq.svg)](https://codeclimate.com/github/gitlabhq/gitlabhq)
-[![Coverage Status](https://coveralls.io/repos/gitlabhq/gitlabhq/badge.svg?branch=master)](https://coveralls.io/r/gitlabhq/gitlabhq?branch=master)
 
 ## Canonical source