remove more "rustdesk" built-in

src/flutter_ffi.rs

@@ -804,6 +804,10 @@ pub fn main_get_app_name_sync() -> SyncReturn<String> {
     SyncReturn(get_app_name())
 }
 
+pub fn main_uri_prefix_sync() -> SyncReturn<String> {
+    SyncReturn(crate::get_uri_prefix())
+}
+
 pub fn main_get_license() -> String {
     get_license()
 }