proxy: Remove the endpoint filter cache (#12488)

## Problem

The endpoint filter cache is still unused because it's not yet reliable
enough to be used. It only consumes a lot of memory.

## Summary of changes

Remove the code. Needs a new design.

neondatabase/cloud#30634

proxy/src/cache/mod.rs

@@ -1,5 +1,4 @@
 pub(crate) mod common;
-pub(crate) mod endpoints;
 pub(crate) mod project_info;
 mod timed_lru;