Remove legacy service count keys

projects_slack_notifications_active and projects_slack_slash_active are
legacy keys that we're not using on any dashboard anymore. We can remove
them.

doc/development/telemetry/usage_ping.md

@@ -501,8 +501,6 @@ appear to be associated to any of the services running, since they all appear to
 | `projects_unify_circuit_active`                           | `counts`                             |               |                  |         |                                                                            |
 | `projects_webex_teams_active`                             | `counts`                             |               |                  |         |                                                                            |
 | `projects_youtrack_active`                                | `counts`                             |               |                  |         |                                                                            |
-| `projects_slack_notifications_active`                     | `counts`                             |               |                  |         |                                                                            |
-| `projects_slack_slash_active`                             | `counts`                             |               |                  |         |                                                                            |
 | `projects_jira_server_active`                             | `counts`                             |               |                  |         |                                                                            |
 | `projects_jira_cloud_active`                              | `counts`                             |               |                  |         |                                                                            |
 | `projects_jira_dvcs_cloud_active`                         | `counts`                             |               |                  |         |                                                                            |

lib/gitlab/usage_data.rb

@@ -343,15 +343,9 @@ module Gitlab
 
       # rubocop: disable CodeReuse/ActiveRecord
       def services_usage
-        results = Service.available_services_names.without('jira').each_with_object({}) do |service_name, response|
+        Service.available_services_names.without('jira').each_with_object({}) do |service_name, response|
           response["projects_#{service_name}_active".to_sym] = count(Service.active.where(template: false, type: "#{service_name}_service".camelize))
-        end
-
-        # Keep old Slack keys for backward compatibility, https://gitlab.com/gitlab-data/analytics/issues/3241
-        results[:projects_slack_notifications_active] = results[:projects_slack_active]
-        results[:projects_slack_slash_active] = results[:projects_slack_slash_commands_active]
-
-        results.merge(jira_usage).merge(jira_import_usage)
+        end.merge(jira_usage).merge(jira_import_usage)
       end
 
       def jira_usage

spec/lib/gitlab/usage_data_spec.rb

@@ -126,8 +126,6 @@ describe Gitlab::UsageData, :aggregate_failures do
       expect(count_data[:jira_imports_projects_count]).to eq(2)
       expect(count_data[:jira_imports_total_imported_count]).to eq(3)
       expect(count_data[:jira_imports_total_imported_issues_count]).to eq(13)
-      expect(count_data[:projects_slack_notifications_active]).to eq(2)
-      expect(count_data[:projects_slack_slash_active]).to eq(1)
       expect(count_data[:projects_slack_active]).to eq(2)
       expect(count_data[:projects_slack_slash_commands_active]).to eq(1)
       expect(count_data[:projects_custom_issue_tracker_active]).to eq(1)

spec/support/helpers/usage_data_helpers.rb

@@ -89,8 +89,6 @@ module UsageDataHelpers
       projects_jira_active
       projects_jira_server_active
       projects_jira_cloud_active
-      projects_slack_notifications_active
-      projects_slack_slash_active
       projects_slack_active
       projects_slack_slash_commands_active
       projects_custom_issue_tracker_active