Simplify calls to have_current_path

In general, we shold check the contents of the page instead of the
current path, since the contents of the page are what users experience.

In one test, the only reason we check the current path additionally to
the contents of the page is to make sure we're still in the management
section.

Checking just that we avoid querying the database after starting the
browser.

spec/system/debates_spec.rb

@@ -317,7 +317,8 @@ describe "Debates" do
 
     click_link "Edit"
 
-    expect(page).to have_current_path(edit_debate_path(Debate.last))
+    expect(page).to have_css "h1", exact_text: "Edit debate"
+    expect(page).to have_field "Debate title", with: "Testing auto link"
     expect(page).not_to have_link("click me")
     expect(page.html).not_to include "<script>alert('hey')</script>"
   end

spec/system/management/proposals_spec.rb

@@ -26,14 +26,13 @@ describe "Proposals" do
 
       expect(page).to have_content "Proposal created successfully."
 
+      expect(page).to have_current_path(/management/)
       expect(page).to have_content "Help refugees"
       expect(page).to have_content "In summary, what we want is..."
       expect(page).to have_content "This is very important because..."
       expect(page).to have_content "https://www.youtube.com/watch?v=yRYFKcMa_Ek"
       expect(page).to have_content user.name
       expect(page).to have_content I18n.l(Date.current)
-
-      expect(page).to have_current_path(management_proposal_path(Proposal.last))
     end
 
     scenario "Should not allow unverified users to create proposals" do

spec/system/proposals_spec.rb

@@ -560,7 +560,7 @@ describe "Proposals" do
 
     click_link "Edit proposal"
 
-    expect(page).to have_current_path(edit_proposal_path(Proposal.last))
+    expect(page).to have_field "Proposal title", with: "Testing auto link"
     expect(page).not_to have_link("click me")
     expect(page.html).not_to include "<script>alert('hey')</script>"
   end