Remove remnants from Infection

Looks like it got lost when migrating to Github actions and removed from
composer.json during a merge up.

I think it would be hard to reintroduce it, and that that should not be
done on the next major branch in any case.

.gitignore

@@ -3,5 +3,4 @@
 /build
 /phpcs.xml
 /.phpcs-cache
-/infection.log
 /.phpunit.result.cache

infection.json.dist

@@ -1,14 +0,0 @@
-{
-    "timeout": 2,
-    "source": {
-        "directories": [
-            "lib"
-        ]
-    },
-    "logs": {
-        "text": "infection.log"
-    },
-    "mutators": {
-        "@default": true
-    }
-}