Remove all magic comments about encoding (#468)

They only work when they are on the first line as pointed out by
#423
(#309 broke that when adding the frozen_string_literal pragma)

UTF-8 is the default (as pointed out by our bot in #467), so remove
them.

Close #423

lib/addressable/idna.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# encoding:utf-8
 #--
 # Copyright (C) Bob Aman
 #

lib/addressable/idna/native.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# encoding:utf-8
 #--
 # Copyright (C) Bob Aman
 #

lib/addressable/idna/pure.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# encoding:utf-8
 #--
 # Copyright (C) Bob Aman
 #

lib/addressable/template.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# encoding:utf-8
 #--
 # Copyright (C) Bob Aman
 #

lib/addressable/uri.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# encoding:utf-8
 #--
 # Copyright (C) Bob Aman
 #

lib/addressable/version.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# encoding:utf-8
 #--
 # Copyright (C) Bob Aman
 #

spec/addressable/idna_spec.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# coding: utf-8
 # Copyright (C) Bob Aman
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");

spec/addressable/net_http_compat_spec.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# coding: utf-8
 # Copyright (C) Bob Aman
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");

spec/addressable/security_spec.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# coding: utf-8
 # Copyright (C) Bob Aman
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");

spec/addressable/template_spec.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# coding: utf-8
 # Copyright (C) Bob Aman
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");

spec/addressable/uri_spec.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-# coding: utf-8
 # Copyright (C) Bob Aman
 #
 #    Licensed under the Apache License, Version 2.0 (the "License");