Makefile.maker.yaml: remove Coveralls

This is required because of
<sapcc/go-makefile-maker#351>.

Author: majewsky

Makefile.maker.yaml

@@ -6,7 +6,6 @@ metadata:
 githubWorkflow:
   ci:
     enabled: true
-    coveralls: true
 
 golang:
   autoupdateableDeps: ^github.com/(?:sapcc|sap-cloud-infrastructure)/