refactor: remove Postal.database_url

lib/postal/config.rb

@@ -86,14 +86,6 @@ module Postal
     end
   end
 
-  def self.database_url
-    if config.main_db
-      "mysql2://#{CGI.escape(config.main_db.username.to_s)}:#{CGI.escape(config.main_db.password.to_s)}@#{config.main_db.host}:#{config.main_db.port}/#{config.main_db.database}?reconnect=true&encoding=#{config.main_db.encoding || 'utf8mb4'}&pool=#{config.main_db.pool_size}"
-    else
-      "mysql2://root@localhost/postal"
-    end
-  end
-
   def self.logger_for(name)
     @loggers ||= {}
     @loggers[name.to_sym] ||= begin