Avoid comments that describe multiple `use` items.

There are some comments describing multiple subsequent `use` items. When
the big `use` reformatting happens some of these `use` items will be
reordered, possibly moving them away from the comment. With this
additional level of formatting it's not really feasible to have comments
of this type. This commit removes them in various ways:

- merging separate `use` items when appropriate;

- inserting blank lines between the comment and the first `use` item;

- outright deletion (for comments that are relatively low-value);

- adding a separate "top-level" comment.

We also entirely skip formatting for four library files that contain
nothing but `pub use` re-exports, where reordering would be painful.

1 files changed, 0 insertions, 1 deletions

diff --git a/library/std/src/rt.rs b/library/std/src/rt.rs
index c0a1c5f5594..82ededa5800 100644
--- a/library/std/src/rt.rs
+++ b/library/std/src/rt.rs
@@ -16,7 +16,6 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 #![allow(unused_macros)]
 
-// Re-export some of our utilities which are expected by other crates.
 pub use crate::panicking::{begin_panic, panic_count};
 pub use core::panicking::{panic_display, panic_fmt};