spec: only load tasks once

When a task is loaded several times, a single call of `task.invoke`
will run the task several times too.

This made `add_annotion_privee_to_procedure_spec` fail when it wasn't
the first task being tested.

spec/lib/rake/2018_03_06_clean_html_textareas_spec.rb

@@ -10,7 +10,6 @@ describe '2018_03_06_clean_html_textareas#clean' do
 
   before do
     Timecop.freeze(champ_date) { champ }
-    TPS::Application.load_tasks
     Timecop.freeze(rake_date) { rake_task.invoke }
     champ.reload
   end

spec/lib/rake/2018_03_29_remove_code_tags_from_mail_templates_spec.rb

@@ -10,7 +10,6 @@ describe '2018_03_29_remove_code_tags_from_mail_templates#clean' do
   let!(:dirty_without_continuation_mail) { create(:without_continuation_mail, body: "<h1>Salut</h1><br>Voici ton email avec une balise <code>--balise--</code>") }
 
   before do
-    TPS::Application.load_tasks
     rake_task.invoke
     dirty_closed_mail.reload
     dirty_initiated_mail.reload

spec/lib/rake/2018_05_14_add_annotation_privee_to_procedure_spec.rb

@@ -24,8 +24,6 @@ describe '2018_05_14_add_annotation_privee_to_procedure' do
   let!(:dossier) { Dossier.create(procedure: procedure, user: user, state: 'brouillon') }
   let(:rake_task) { Rake::Task['2018_05_14_add_annotation_privee_to_procedure:add'] }
 
-  before(:all) { TPS::Application.load_tasks }
-
   before do
     ENV['PROCEDURE_ID'] = procedure.id.to_s
     rake_task.invoke

spec/spec_helper.rb

@@ -69,6 +69,8 @@ end
 
 DatabaseCleaner.strategy = :transaction
 
+TPS::Application.load_tasks
+
 SIADETOKEN = :valid_token if !defined? SIADETOKEN
 
 include Warden::Test::Helpers