use Array#uniq in AM instead of deprecated Array#uniq_by

actionmailer/lib/action_mailer.rb

@@ -31,7 +31,6 @@
 # Common Active Support usage in Action Mailer
 require 'active_support/core_ext/class'
 require 'active_support/core_ext/object/blank'
-require 'active_support/core_ext/array/uniq_by'
 require 'active_support/core_ext/module/attr_internal'
 require 'active_support/core_ext/module/delegation'
 require 'active_support/core_ext/string/inflections'

actionmailer/lib/action_mailer/base.rb

@@ -708,7 +708,7 @@ def collect_responses_and_parts_order(headers) #:nodoc:
 
     def each_template(paths, name, &block) #:nodoc:
       templates = lookup_context.find_all(name, Array.wrap(paths))
-      templates.uniq_by { |t| t.formats }.each(&block)
+      templates.uniq { |t| t.formats }.each(&block)
     end
 
     def create_parts_from_responses(m, responses) #:nodoc: