Turbopack: chore: Remove dead RouteMatcher stuff (#85784)

Turns out this is all dead code, so delete it!

It looks like this was added back in vercel/turborepo#3448, probably when Turbopack was trying to rewrite larger parts of Next.js than ended up happening.

Author: bgw

crates/next-core/src/lib.rs

@@ -27,7 +27,6 @@ mod next_import_map;
 pub mod next_manifests;
 pub mod next_pages;
 mod next_root_params;
-mod next_route_matcher;
 pub mod next_server;
 pub mod next_server_component;
 pub mod next_server_utility;