Use JavaScript in system tests by default

JavaScript is used by about 98% of web users, so by testing without it
enabled, we're only testing that the application works for a very
reduced number of users.

We proceeded this way in the past because CONSUL started using Rails 4.2
and truncating the database between JavaScript tests with database
cleaner, which made these tests terribly slow.

When we upgraded to Rails 5.1 and introduced system tests, we started
using database transactions in JavaScript tests, making these tests much
faster. So now we can use JavaScript tests everywhere without critically
slowing down our test suite.

spec/system/admin/homepage/homepage_spec.rb

@@ -26,7 +26,7 @@ describe "Homepage", :admin do
   end
 
   context "Feeds" do
-    scenario "Proposals", :js do
+    scenario "Proposals" do
       5.times { create(:proposal) }
 
       visit admin_homepage_path
@@ -46,7 +46,7 @@ describe "Homepage", :admin do
       expect(page).not_to have_css("#feed_proposals.medium-8")
     end
 
-    scenario "Debates", :js do
+    scenario "Debates" do
       5.times { create(:debate) }
 
       visit admin_homepage_path
@@ -65,7 +65,7 @@ describe "Homepage", :admin do
       expect(page).not_to have_css("#feed_debates.medium-4")
     end
 
-    scenario "Proposals and debates", :js do
+    scenario "Proposals and debates" do
       3.times { create(:proposal) }
       3.times { create(:debate) }
 
@@ -94,7 +94,7 @@ describe "Homepage", :admin do
       end
     end
 
-    scenario "Processes", :js do
+    scenario "Processes" do
       5.times { create(:legislation_process) }
 
       visit admin_homepage_path
@@ -112,7 +112,7 @@ describe "Homepage", :admin do
     xscenario "Deactivate"
   end
 
-  scenario "Cards", :js do
+  scenario "Cards" do
     card1 = create(:widget_card, label: "Card1 label",
                                  title: "Card1 text",
                                  description: "Card1 description",