cmake: CMakeLists.txt: remove conncetion_notifier.cc
cmake: CMakeLists.txt: remove conncetion_notifier.cc

It was removed in 3aa05f7f036846751c2691500fb4cc8b54e36921.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20220406110512.3731011-2-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla