Remove deeply-nested{,-async,-closures}.

They have been superseded by `deeply-nested-multi`.

Author: nnethercote

collector/benchmarks/README.md

@@ -66,12 +66,6 @@ compiler in interesting ways.
   caused [poor performance](https://github.com/rust-lang/rust/issues/32278) in
   the past.
 - **ctfe-stress-4**: A stress test for compile-time function evaluation.
-- **deeply-nested**: A small program that caused [exponential
-  behavior](https://github.com/rust-lang/rust/issues/38528) in the past.
-- **deeply-nested-async**: Another small program that caused [exponential
-  behavior](https://github.com/rust-lang/rust/issues/75992) in the past.
-- **deeply-nested-closures**: A small program that caused [exponential
-  behavior](https://github.com/rust-lang/rust/issues/72408) in the past.
 - **deeply-nested-multi**: A small program containing multiple examples 
   ([one](https://github.com/rust-lang/rust/issues/38528),
   [two](https://github.com/rust-lang/rust/issues/72408),