Remove outdated issue2478 marker

Looks like this works on Windows nowadays.
See #2478

pytest.ini

@@ -26,7 +26,6 @@ markers =
     js_prompt: Tests needing to display a javascript prompt
     this: Used to mark tests during development
     no_invalid_lines: Don't fail on unparseable lines in end2end tests
-    issue2478: Tests which are broken on Windows with QtWebEngine, https://github.com/qutebrowser/qutebrowser/issues/2478
     issue3572: Tests which are broken with QtWebEngine and Qt 5.10, https://github.com/qutebrowser/qutebrowser/issues/3572
     qtbug60673: Tests which are broken if the conversion from orange selection to real selection  is flaky
     qtbug80085: Tests which are broken on Qt 5.14 due to a missing renderProcessTerminated signal

tests/conftest.py

@@ -101,10 +101,6 @@ def _apply_platform_markers(config, item):
          sys.getfilesystemencoding() == 'ascii',
          "Skipped because of ASCII locale"),
 
-        ('issue2478',
-         pytest.mark.xfail,
-         utils.is_windows and config.webengine,
-         "Broken with QtWebEngine on Windows"),
         ('issue3572',
          pytest.mark.xfail,
          (qtutils.version_check('5.10', compiled=False, exact=True) or

tests/end2end/features/prompts.feature

@@ -177,7 +177,6 @@ Feature: Prompts
         Then the error "Certificate error: *" should be shown
         And the page should contain the plaintext "Hello World via SSL!"
 
-    @issue2478
     Scenario: SSL error with content.ssl_strict = true
         When I clear SSL errors
         And I set content.ssl_strict to true
@@ -193,7 +192,6 @@ Feature: Prompts
         And I wait until the SSL page finished loading
         Then the page should contain the plaintext "Hello World via SSL!"
 
-    @issue2478
     Scenario: SSL error with content.ssl_strict = ask -> no
         When I clear SSL errors
         And I set content.ssl_strict to ask
@@ -202,7 +200,6 @@ Feature: Prompts
         And I run :prompt-accept no
         Then a SSL error page should be shown
 
-    @issue2478
     Scenario: SSL error with content.ssl_strict = ask -> abort
         When I clear SSL errors
         And I set content.ssl_strict to ask