Remove high cardinality Prometheus metric

The metric was used to correlate Gitaly requests to the Rails controller
and action combination. However, Kibana provides better observability in
this specific metric, and can handle hig cardinality much better.

There's no dashboard in Grafana that currently depends on this metric
being exposed.

lib/gitlab/gitaly_client.rb

@@ -33,11 +33,6 @@ module Gitlab
 
     MUTEX = Mutex.new
 
-    define_histogram :gitaly_controller_action_duration_seconds do
-      docstring "Gitaly endpoint histogram by controller and action combination"
-      base_labels Gitlab::Metrics::Transaction::BASE_LABELS.merge(gitaly_service: nil, rpc: nil)
-    end
-
     def self.stub(name, storage)
       MUTEX.synchronize do
         @stubs ||= {}
@@ -161,10 +156,6 @@ module Gitlab
 
       # Keep track, separately, for the performance bar
       self.query_time += duration
-      gitaly_controller_action_duration_seconds.observe(
-        current_transaction_labels.merge(gitaly_service: service.to_s, rpc: rpc.to_s),
-        duration)
-
       if peek_enabled?
         add_call_details(feature: "#{service}##{rpc}", duration: duration, request: request_hash, rpc: rpc,
                          backtrace: Gitlab::Profiler.clean_backtrace(caller))