Remove redundant I18nContent scope

Since two records cannot have the same key, having a scope that will
always return just one record is the same as using `find_by_key`.

app/models/i18n_content.rb

@@ -1,7 +1,4 @@
 class I18nContent < ApplicationRecord
-
-  scope :by_key,          ->(key) { where(key: key) }
-
   validates :key, uniqueness: true
 
   translates :value, touch: true

config/initializers/i18n_translation.rb

@@ -9,7 +9,7 @@ module ActionView
       def t(key, options = {})
         current_locale = options[:locale].presence || I18n.locale
 
-        i18_content = I18nContent.by_key(key).first
+        i18_content = I18nContent.find_by_key(key)
         translation = I18nContentTranslation.where(i18n_content_id: i18_content&.id,
                                                    locale: current_locale).first&.value
         translation.presence || translate(key, options)

spec/models/i18n_content_spec.rb

@@ -14,21 +14,6 @@ RSpec.describe I18nContent, type: :model do
     expect(i18n_content.errors.size).to eq(1)
   end
 
-  context "Scopes" do
-    it "return one record when #by_key is used" do
-      content      = create(:i18n_content)
-      key          = "debates.form.debate_title"
-      debate_title = create(:i18n_content, key: key)
-
-      expect(I18nContent.all.size).to eq(2)
-
-      query = I18nContent.by_key(key)
-
-      expect(query.size).to eq(1)
-      expect(query).to eq([debate_title])
-    end
-  end
-
   context "Globalize" do
     it "translates key into multiple languages" do
       key = "devise_views.mailer.confirmation_instructions.welcome"