Remove admin check

This was non-functional for over a year

src/admin/mod.rs

@@ -7,7 +7,6 @@ mod tests;
 pub(crate) mod utils;
 
 pub(crate) mod appservice;
-pub(crate) mod check;
 pub(crate) mod debug;
 pub(crate) mod federation;
 pub(crate) mod media;