AK+Everywhere: Replace "protocol" with "scheme" url helpers

URL had properly named replacements for protocol(), set_protocol() and
create_with_file_protocol() already. This patch removes these function
and updates all call sites to use the functions named according to the
specification.

See https://url.spec.whatwg.org/#concept-url-scheme

Userland/Applications/Spreadsheet/HelpWindow.cpp

@@ -81,7 +81,7 @@ HelpWindow::HelpWindow(GUI::Window* parent)
 
     m_webview = splitter.add<WebView::OutOfProcessWebView>();
     m_webview->on_link_click = [this](auto& url, auto&, auto&&) {
-        VERIFY(url.protocol() == "spreadsheet");
+        VERIFY(url.scheme() == "spreadsheet");
         if (url.host() == "example") {
             auto entry = LexicalPath::basename(url.path());
             auto doc_option = m_docs.get(entry);