Remove Unicorn detection in pid provider

Drop unicorn-related code from Prometheus Pid Provider. Also update
ruby_sampler accordingly.

Changelog: removed

lib/gitlab/metrics/samplers/ruby_sampler.rb

 # frozen_string_literal: true
 
-require 'prometheus/client/support/unicorn'
-
 module Gitlab
   module Metrics
     module Samplers

lib/prometheus/pid_provider.rb

@@ -7,8 +7,6 @@ module Prometheus
     def worker_id
       if Gitlab::Runtime.sidekiq?
         sidekiq_worker_id
-      elsif Gitlab::Runtime.unicorn?
-        unicorn_worker_id
       elsif Gitlab::Runtime.puma?
         puma_worker_id
       else
@@ -26,16 +24,6 @@ module Prometheus
       end
     end
 
-    def unicorn_worker_id
-      if matches = process_name.match(/unicorn.*worker\[([0-9]+)\]/)
-        "unicorn_#{matches[1]}"
-      elsif process_name =~ /unicorn/
-        "unicorn_master"
-      else
-        unknown_process_id
-      end
-    end
-
     def puma_worker_id
       if matches = process_name.match(/puma.*cluster worker ([0-9]+):/)
         "puma_#{matches[1]}"

spec/lib/prometheus/pid_provider_spec.rb

@@ -28,66 +28,6 @@ RSpec.describe Prometheus::PidProvider do
       end
     end
 
-    context 'when running in Unicorn mode' do
-      before do
-        allow(Gitlab::Runtime).to receive(:unicorn?).and_return(true)
-
-        expect(described_class).to receive(:process_name)
-          .at_least(:once)
-          .and_return(process_name)
-      end
-
-      context 'when unicorn master is specified in process name' do
-        context 'when running in Omnibus' do
-          context 'before the process was renamed' do
-            let(:process_name) { "/opt/gitlab/embedded/bin/unicorn"}
-
-            it { is_expected.to eq 'unicorn_master' }
-          end
-
-          context 'after the process was renamed' do
-            let(:process_name) { "unicorn master -D -E production -c /var/opt/gitlab/gitlab-rails/etc/unicorn.rb /opt/gitlab/embedded/service/gitlab-rails/config.ru" }
-
-            it { is_expected.to eq 'unicorn_master' }
-          end
-        end
-
-        context 'when in development env' do
-          context 'before the process was renamed' do
-            let(:process_name) { "path_to_bindir/bin/unicorn_rails"}
-
-            it { is_expected.to eq 'unicorn_master' }
-          end
-
-          context 'after the process was renamed' do
-            let(:process_name) { "unicorn_rails master -c /gitlab_dir/config/unicorn.rb -E development" }
-
-            it { is_expected.to eq 'unicorn_master' }
-          end
-        end
-      end
-
-      context 'when unicorn worker id is specified in process name' do
-        context 'when running in Omnibus' do
-          let(:process_name) { "unicorn worker[1] -D -E production -c /var/opt/gitlab/gitlab-rails/etc/unicorn.rb /opt/gitlab/embedded/service/gitlab-rails/config.ru" }
-
-          it { is_expected.to eq 'unicorn_1' }
-        end
-
-        context 'when in development env' do
-          let(:process_name) { "unicorn_rails worker[1] -c gitlab_dir/config/unicorn.rb -E development" }
-
-          it { is_expected.to eq 'unicorn_1' }
-        end
-      end
-
-      context 'when no specified unicorn master or worker id in process name' do
-        let(:process_name) { "bin/unknown_process"}
-
-        it { is_expected.to eq "process_#{Process.pid}" }
-      end
-    end
-
     context 'when running in Puma mode' do
       before do
         allow(Gitlab::Runtime).to receive(:puma?).and_return(true)