Fix mutant configuration

* Remove config/mutant.yml devtools task is not flexible enough
* Add Mutant::Meta* to eclusionx (test code not relevant for the tools
  value).

Rakefile

@@ -14,6 +14,7 @@ namespace :metrics do
       --include lib
       --require mutant
       --since HEAD~1
+      --ignore-subject Mutant::Meta*
       --
       Mutant*
     ]) or fail 'Mutant task is not successful'

config/mutant.yml

@@ -1,14 +0,0 @@
-name: mutant
-namespace: Mutant
-zombify: true
-expect_coverage: 62.08
-ignore_subjects:
-# Mutation causes infinite runtime
-- Mutant::Runner.lookup
-# Suboptimal test selection strategy (will be fixed soon) causes timeouts on CI
-- Mutant::Zombifier*
-- Mutant::Reporter*
-- Mutant::CLI*
-- Mutant.singleton_subclass_instance
-# Executing this has undefined behavior with the zombifier
-- Mutant.zombify