Remove the function make_keyspace_name() that was never used.
We *could* have used this function, but we didn't, and it had
had an inconvenient API. If we later want to de-duplicate the
several copies of "executor::KEYSPACE_NAME_PREFIX + table_name"
we have in the code, we can do it with a better API.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
62b6179c88