Remove custom panic handler.

This was introduced because Tokio would swallow panics. This is still
the case, but this panic handler causes more problems than it solves.
It requires people to know how to use debuggers to inspect stacktraces.

TODO:
- Fix Tokio to not swallow errors.
- Be vigilant in the intrim to not introduce broken tests due to this
  unfortunate "feature" of tokio.

src/main.rs

@@ -77,14 +77,6 @@ fn print_err_and_exit(err: js_errors::JSError) {
 }
 
 fn main() {
-  // Rust does not die on panic by default. And -Cpanic=abort is broken.
-  // https://github.com/rust-lang/cargo/issues/2738
-  // Therefore this hack.
-  std::panic::set_hook(Box::new(|panic_info| {
-    eprintln!("{}", panic_info.to_string());
-    std::process::abort();
-  }));
-
   log::set_logger(&LOGGER).unwrap();
   let args = env::args().collect();
   let (flags, rest_argv, usage_string) =