Fix benchmarks! macro for non dispatchable code (#5100)

* Init allowing non dispatchable closure to be benchmarked.

* Remove example, add it in timestamp

* Fix nits.

* Move test to example.

* Update frame/example/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update frame/example/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Apply review suggestion: move test to benchmarking crate.

* Update frame/benchmarking/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Remove unused imports.

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Benjamin Kampmann <ben.kampmann@googlemail.com>