Remove leftovers from broken becnhmark

While I tried to land COUCHDB-1432 on 1..x.x it turned out that
/benches/run is broken in several places for a longer time and
nobody noticed: When trying to fix it (adding a file called
test_setup.js) to the template, we will get the next error.

As nobody noticed that it is broken for a longer time it seems we
currently have no need for benchmarks, and if we have that need,
we should add new ones which reflect our current needs and are
compatible with 2.0 too.

This removes the leftovers of the benchmark which is also broken
on 1.6.x for a longer, unknown time which was already deleted in
parts for 2.0