Remove the repository_ancestor_calls_total counter

We've validated that the we're hitting the cache, so this particular
counter isn't really needed anymore.

app/models/repository.rb

@@ -927,22 +927,12 @@ class Repository
   def ancestor?(ancestor_id, descendant_id)
     return false if ancestor_id.nil? || descendant_id.nil?
 
-    counter = Gitlab::Metrics.counter(
-      :repository_ancestor_calls_total,
-      'The number of times we call Repository#ancestor with valid arguments')
-    cache_hit = true
-
     cache_key = "ancestor:#{ancestor_id}:#{descendant_id}"
-    result = request_store_cache.fetch(cache_key) do
+    request_store_cache.fetch(cache_key) do
       cache.fetch(cache_key) do
-        cache_hit = false
         raw_repository.ancestor?(ancestor_id, descendant_id)
       end
     end
-
-    counter.increment(cache_hit: cache_hit.to_s)
-
-    result
   end
 
   def fetch_as_mirror(url, forced: false, refmap: :all_refs, remote_name: nil, prune: true)

spec/models/repository_spec.rb

@@ -2450,15 +2450,6 @@ describe Repository do
         2.times { repository.ancestor?(commit.id, ancestor.id) }
       end
 
-      it 'increments a counter with cache hits' do
-        counter = Gitlab::Metrics.counter(:repository_ancestor_calls_total, 'Repository ancestor calls')
-
-        expect do
-          2.times { repository.ancestor?(commit.id, ancestor.id) }
-        end.to change { counter.get(cache_hit: 'true') }.by(1)
-                 .and change { counter.get(cache_hit: 'false') }.by(1)
-      end
-
       it 'returns the value from the request store' do
         repository.__send__(:request_store_cache).write(cache_key, "it's apparent")