Reapply "perf(transport): remove Server::timers (#1784)" (#1800) (#1902)

This reverts commit 342e4e7.

With #1878 merged and
https://bugzilla.mozilla.org/show_bug.cgi?id=1895319 available, one can now
reapply the patch removing `Server::timers`.

More specifically, the actual bug fix on mozilla-central side:

``` rust
let output = if self.response_to_send.is_empty() {
    output
} else {
    // In case there are pending responses to send, make sure a reasonable
    // callback is returned.
    const MIN_INTERVAL: Duration = Duration::from_millis(100);

    match output {
        Output::None => Output::Callback(MIN_INTERVAL),
        o @ Output::Datagram(_) => o,
        Output::Callback(d) => Output::Callback(min(d, MIN_INTERVAL)),
    }
};
```

See https://phabricator.services.mozilla.com/D209574.

neqo-common/Cargo.toml

@@ -35,7 +35,3 @@ features = ["timeapi"]
 [lib]
 # See https://github.com/bheisler/criterion.rs/blob/master/book/src/faq.md#cargo-bench-gives-unrecognized-option-errors-for-valid-command-line-options
 bench = false
-
-[[bench]]
-name = "timer"
-harness = false

neqo-common/src/lib.rs

@@ -16,7 +16,6 @@ pub mod hrtime;
 mod incrdecoder;
 pub mod log;
 pub mod qlog;
-pub mod timer;
 pub mod tos;
 
 use std::fmt::Write;