Browser+WebDriver: Set the initial URL to about:blank from WebDriver

We already do this for headless-browser. There's no need to open any URL
other than about:blank when starting a WebDriver session. We should also
do this from WebDriver code, rather than in special logic in Browser's
main.cpp.

Ladybird/WebDriver/main.cpp

@@ -36,6 +36,7 @@ static ErrorOr<pid_t> launch_browser(DeprecatedString const& socket_path)
         Array {
             "--webdriver-content-path",
             socket_path.characters(),
+            "about:blank",
         });
 }
 

Userland/Applications/Browser/main.cpp

@@ -114,9 +114,6 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     TRY(Desktop::Launcher::add_allowed_url(URL::create_with_file_scheme(Core::StandardPaths::downloads_directory())));
     TRY(Desktop::Launcher::seal_allowlist());
 
-    if (!Browser::g_webdriver_content_ipc_path.is_empty())
-        specified_urls.empend("about:blank");
-
     TRY(Core::System::unveil("/tmp/session/%sid/portal/filesystemaccess", "rw"));
     TRY(Core::System::unveil("/tmp/session/%sid/portal/filesystemaccess", "rw"));
     TRY(Core::System::unveil("/tmp/session/%sid/portal/image", "rw"));

Userland/Services/WebDriver/main.cpp

@@ -20,6 +20,7 @@ static ErrorOr<pid_t> launch_browser(DeprecatedString const& socket_path)
         Array {
             "--webdriver-content-path",
             socket_path.characters(),
+            "about:blank",
         });
 }