Revert "regexp: add the Fanout benchmark

This is a copy of the "FANOUT" benchmark recently added to RE2 with the
following comment:

    // This has quite a high degree of fanout.
    // NFA execution will be particularly slow.

Most of the benchmarks on the regexp package have very little fanout and
are designed for comparing the regexp package's NFA with backtracking
engines found in other regular expression libraries. This benchmark
exercises the performance of the NFA on expressions with high fanout.Reviewed-on: https://go-review.googlesource.com/24846


Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
"

This reverts commit fc803874.

Reason for revert: Breaks the -race build because the benchmark takes too long to run.

Change-Id: I6ed4b466f74a4108d8bcd5b019b9abe971eb483e
Reviewed-on: https://go-review.googlesource.com/24861


Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>