Use single presenter for everything

app/models/project_services/chat_slash_commands_service.rb

@@ -33,10 +33,10 @@ class ChatSlashCommandsService < Service
     user = find_chat_user(params)
     unless user
       url = authorize_chat_name_url(params)
-      return presenter.authorize_chat_name(url)
+      return Gitlab::ChatCommands::Presenter.authorize_chat_name(url)
     end
 
-    Gitlab::ChatCommands::Command.new(presenter, project, user, params).execute
+    Gitlab::ChatCommands::Command.new(project, user, params).execute
   end
 
   private
@@ -48,8 +48,4 @@ class ChatSlashCommandsService < Service
   def authorize_chat_name_url(params)
     ChatNames::AuthorizeUserService.new(self, params).execute
   end
-
-  def presenter
-    throw NotImplementedError
-  end
 end

app/models/project_services/mattermost_slash_commands_service.rb

@@ -18,8 +18,4 @@ class MattermostSlashCommandsService < ChatService
   def to_param
     'mattermost_slash_commands'
   end
-
-  def presenter
-    Gitlab::ChatCommands::Presenters::Mattermost.new
-  end
 end

app/models/project_services/slack_slash_commands_service.rb

@@ -12,8 +12,4 @@ class SlackSlashCommandsService < ChatSlashCommandsService
   def to_param
     'slack_slash_commands'
   end
-
-  def presenter
-    Gitlab::ChatCommands::Presenters::Mattermost.new
-  end
 end