remove code coverage badge (#3352)

README.md

@@ -1,7 +1,5 @@
 # Firefox Monitor Server
 
-[![Coverage Status](https://coveralls.io/repos/github/mozilla/blurts-server/badge.svg?branch=main)](https://coveralls.io/github/mozilla/blurts-server?branch=main)
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 ## Summary
 
 Firefox Monitor notifies users when their credentials have been compromised in a data breach.