Remove unnecessary enconding magic comment

This comment isn't necessary since Ruby 2.0, where UTF-8 became the
default encoding.

I've found this issue thanks to the EmptyLineAfterMagicComment rubocop
rule.

db/seeds.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 # Default admin user (change password after first deploy to a server!)
 if Administrator.count == 0 && !Rails.env.test?
   admin = User.create!(username: "admin", email: "admin@consul.dev", password: "12345678",

spec/features/debates_spec.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 require "rails_helper"
 
 describe "Debates" do

spec/features/proposal_ballots_spec.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 require "rails_helper"
 
 describe "Proposal ballots" do

spec/features/proposals_spec.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 require "rails_helper"
 
 describe "Proposals" do

spec/mailers/devise_mailer_spec.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 require "rails_helper"
 
 describe DeviseMailer do

spec/models/debate_spec.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 require "rails_helper"
 
 describe Debate do

spec/models/proposal_spec.rb

@@ -1,4 +1,3 @@
-# coding: utf-8
 require "rails_helper"
 
 describe Proposal do