Remove obsolete "let" blocks in tests setup

These blocks are no longer used:

* `allowed_phase_list` isn't used since commit 04605d5d5
* `level_two_user` isn't used since commit 26d14cbd0
* `heading` in `budgets/stats_spec` was added in c2457e36a but never
  used
* `translatable` was added in 44d137a4c but it's overwritten in all the
  contexts.
* `annotation` isn't used since commit 79d00e7b9
* `admin` in `tags/budget_investments_spec` isn't used since 8a2e15980
* `budget` in `welcome_spec` was added in 87be6f302 but never used

spec/system/admin/translatable_spec.rb

@@ -130,8 +130,6 @@ describe "Admin edit translatable records", :admin do
   end
 
   context "Add an invalid translation" do
-    let(:translatable) { create(:budget_investment) }
-
     context "Input field" do
       let(:translatable) { create(:budget, main_link_url: "https://consuldemocracy.org") }
 

spec/system/budgets/budgets_spec.rb

@@ -2,8 +2,6 @@ require "rails_helper"
 
 describe "Budgets" do
   let(:budget) { create(:budget) }
-  let(:level_two_user)     { create(:user, :level_two) }
-  let(:allowed_phase_list) { ["balloting", "reviewing_ballots", "finished"] }
 
   context "Load" do
     before { budget.update(slug: "budget_slug") }

spec/system/budgets/stats_spec.rb

@@ -2,7 +2,6 @@ require "rails_helper"
 
 describe "Stats" do
   let(:budget) { create(:budget, :finished) }
-  let(:heading) { create(:budget_heading, budget: budget, price: 1000) }
 
   context "Load" do
     before { budget.update(slug: "budget_slug") }

spec/system/comments/legislation_annotations_spec.rb

@@ -2,7 +2,6 @@ require "rails_helper"
 
 describe "Commenting legislation annotations" do
   let(:user) { create(:user) }
-  let(:annotation) { create(:legislation_annotation, author: user) }
 
   describe "Merged comment threads" do
     let!(:draft_version) { create(:legislation_draft_version, :published) }

spec/system/tags/budget_investments_spec.rb

@@ -10,7 +10,6 @@ describe "Tags" do
   end
   let!(:tag_medio_ambiente) { create(:tag, :category, name: "Medio Ambiente") }
   let!(:tag_economia) { create(:tag, :category, name: "Economía") }
-  let(:admin) { create(:administrator).user }
 
   scenario "Index" do
     earth = create(:budget_investment, heading: heading, tag_list: tag_medio_ambiente.name)

spec/system/welcome_spec.rb

@@ -1,8 +1,6 @@
 require "rails_helper"
 
 describe "Welcome screen" do
-  let(:budget) { create(:budget) }
-
   it_behaves_like "remotely_translatable", :proposal, "root_path", {}
   it_behaves_like "remotely_translatable", :debate, "root_path", {}
   it_behaves_like "remotely_translatable", :legislation_process, "root_path", {}