doc: remove benchmarking WG
doc: remove benchmarking WG

Benchmarking WG has been de-chartered, remove
references to it.

Refs: https://github.com/nodejs/TSC/pull/955

Signed-off-by: Michael Dawson <697f19bdc6386e09c0d34238f49474ef87a73bae@devrus.com>

nodejs/new.nodejs.org,nodejs/new.nodejs.org