internal: drop latest requests tracking

From the dawn of time, when dinosaurs roamed the and we didn't have
hierarchical profiling, there was the `latest_requests` infra we used to
track the time of ten last requests.

Today, no one is actually using it and, what's more, it itself became
pretty useless -- LSP grew way more chatty, and 10 requests don't really
paint any kind of picture.

Personally, it's been years since I last looked at latest requests in
the status output.

So, let's remove a tiny bit of state from the big ball of complexity
that is `GlobalState` and `main_loop`!

crates/rust-analyzer/src/lib.rs

@@ -30,7 +30,6 @@ mod semantic_tokens;
 mod markdown;
 mod diagnostics;
 mod line_index;
-mod request_metrics;
 mod lsp_utils;
 mod thread_pool;
 mod mem_docs;