tests: fstream: remove obsolete comments about running in background
tests: fstream: remove obsolete comments about running in background

Comments about running in background and signaling when done
should have been removed in 49b2e5d97d77dcf57a2e30c3872c2b73718776c9

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20200602104333.384381-1-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

syuu1228/seastar,dreamsxin/seastar,syuu1228/seastar,cloudius-systems/seastar,avikivity/seastar,scylladb/seastar,syuu1228/seastar,scylladb/seastar,scylladb/seastar,cloudius-systems/seastar,cloudius-systems/seastar,dreamsxin/seastar,dreamsxin/seastar,avikivity/seastar,avikivity/seastar