Remove setup_callbacks_and_run_in_default_thread_pool_with_globals().

It's a very thin wrapper around
`setup_callbacks_and_run_in_thread_pool_with_globals()` and it has a
single call site.

src/librustc_interface/interface.rs

@@ -17,7 +17,6 @@ use rustc_session::early_error;
 use rustc_session::lint;
 use rustc_session::parse::{CrateConfig, ParseSess};
 use rustc_session::{DiagnosticOutput, Session};
-use rustc_span::edition;
 use rustc_span::source_map::{FileLoader, FileName};
 use std::path::PathBuf;
 use std::result;
@@ -208,13 +207,3 @@ pub fn run_compiler<R: Send>(mut config: Config, f: impl FnOnce(&Compiler) -> R
         || create_compiler_and_run(config, f),
     )
 }
-
-pub fn setup_callbacks_and_run_in_default_thread_pool_with_globals<R: Send>(
-    edition: edition::Edition,
-    f: impl FnOnce() -> R + Send,
-) -> R {
-    // the 1 here is duplicating code in config.opts.debugging_opts.threads
-    // which also defaults to 1; it ultimately doesn't matter as the default
-    // isn't threaded, and just ignores this parameter
-    util::setup_callbacks_and_run_in_thread_pool_with_globals(edition, 1, &None, f)
-}

src/librustdoc/lib.rs

@@ -431,8 +431,10 @@ fn main_args(args: &[String]) -> MainResult {
         Ok(opts) => opts,
         Err(code) => return if code == 0 { Ok(()) } else { Err(ErrorReported) },
     };
-    rustc_interface::interface::setup_callbacks_and_run_in_default_thread_pool_with_globals(
+    rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals(
         options.edition,
+        1, // this runs single-threaded, even in a parallel compiler
+        &None,
         move || main_options(options),
     )
 }