Allow users to remove their support on investments

Note we don't cast negative votes when users remove their support. That
way we provide compatibility for institutions who have implemented real
negative votes (in case there are / will be any), and we also keep the
database meaningful: it's not that users downvoted something; they
simply removed their upvote.

Co-Authored-By: Javi Martín <javim@elretirao.net>
Co-Authored-By: Julian Nicolas Herrero <microweb10@gmail.com>

spec/system/budgets/investments_spec.rb

@@ -1177,6 +1177,48 @@ describe "Budget Investments" do
         expect(page).to have_content "SUPPORTS"
       end
     end
+
+    scenario "Remove a support from show view" do
+      investment = create(:budget_investment, budget: budget)
+
+      login_as(author)
+      visit budget_investment_path(budget, investment)
+
+      within("aside") do
+        expect(page).to have_content "No supports"
+
+        click_button "Support"
+
+        expect(page).to have_content "1 support"
+        expect(page).to have_content "You have already supported this investment project."
+
+        click_button "Remove your support"
+
+        expect(page).to have_content "No supports"
+        expect(page).to have_button "Support"
+      end
+    end
+
+    scenario "Remove a support from index view" do
+      investment = create(:budget_investment, budget: budget)
+
+      login_as(author)
+      visit budget_investments_path(budget)
+
+      within("#budget_investment_#{investment.id}") do
+        expect(page).to have_content "No supports"
+
+        click_button "Support"
+
+        expect(page).to have_content "1 support"
+        expect(page).to have_content "You have already supported this investment project."
+
+        click_button "Remove your support"
+
+        expect(page).to have_content "No supports"
+        expect(page).to have_button "Support"
+      end
+    end
   end
 
   context "Evaluating Phase" do