future: Move some predicates to any::
future: Move some predicates to any::

They were defined in future_state_base but only used the _u member
variable. Move them directly to the "any" union. This is a bit more
idiomatic and will allow implementing a few other functions there.

Signed-off-by: Rafael Ávila de Espíndola <1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>

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