WPT clear-cache.https.html: clarify and cleanup test function

Clearing cookies isn't necessary, because the test doesn't rely on cookies anymore.

Differential Revision: https://phabricator.services.mozilla.com/D234941

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1942778
gecko-commit: 5634203a9e231baac99c8dc43d74445dd600d64c
gecko-reviewers: anti-tracking-reviewers, emz

clear-site-data/clear-cache.https.html

@@ -8,12 +8,12 @@
 
 // Here's the set-up for this test:
 // Step 1 (main window) Open first window with first url putting some resource
-//                       into the cache and maybe receiving clear-site-data header
-// Step 2 (first window) Message first window with uuid
+//                      into the cache and maybe receiving clear-site-data header
+// Step 2 (first window) Message main window with uuid
 // Step 3 (main window) Open second window with second url
-// Step 4 (second window) Message first window with uuid (either cached or non-cached)
+// Step 4 (second window) Message main window with uuid (either cached or non-cached)
 // Optional Step 5 (main window) Open third window with third url
-// Optional Step 6 (third window) Message first window with uuid (either cached or non-cached)
+// Optional Step 6 (third window) Message main window with uuid (either cached or non-cached)
 // Step 7 (main window): Assert first and last uuid not equal due to `clear-site-data: "cache"` header
 function test_cache_clear(test, params1, params2, params3) {
     let cache_helper = "cache_helper=" + self.crypto.randomUUID() + "&";
@@ -60,8 +60,6 @@
         // Step 1
         let first_window = window.open(firstUrl);
         test.add_cleanup(first_window.close);
-        // tests are using cookies to differentiate between requests
-        test.add_cleanup(test_driver.delete_all_cookies)
     });
 }