appid: Switch to checking via API again

Summary parsing requires users to set up both Flathub stable and beta
remotes, which is a hard ask.

flatpak_builder_lint/checks/appid.py

@@ -58,7 +58,7 @@ def _validate(self, appid: Optional[str], is_extension: bool) -> None:
                 return
             if split[-1] == "Devel":
                 return
-            if domainutils.is_appid_on_flathub(appid):
+            if domainutils.is_app_on_flathub(appid):
                 return
             if appid.startswith(domainutils.code_hosts):
                 if domainutils.get_proj_url(appid) is None: