Remove redundant assert_selector in system test to avoid flakiness

I was seeing some flakiness with these selectors asserting the
presence of `h1` and `h2`. I suspect this might be due to the use of
Turbo to replace the page DOM rather than a full page reload. Since
the other assert_text calls confirm that we're on the correct page, I
think I can safely remove these without losing coverage.

test/system/buying_an_album_test.rb

@@ -13,11 +13,7 @@ class BuyingAnAlbumTest < ApplicationSystemTestCase
     click_link @album.artist.name
     click_link @album.title
 
-    assert_selector 'h1', text: @album.title
-    assert_selector 'h2', text: @album.artist.name
-
     assert_text "1. #{@album.tracks.first.title}"
-
     assert_text @album.about.gsub(/^\s+/, '')
     assert_text @album.credits.gsub(/^\s+/, '')
   end