async/deref_path: eliminate static variable that keeps strong actor ref
async/deref_path: eliminate static variable that keeps strong actor ref

Refactor.
1. Use `anon_async_api_mixin`.
2. Implement scheme:
  a) spawn actor with `lazy_init` flag & store strong ref in local variable on stack;
  b) send message to it;
  c) forget actor and return.

Actor is spawned from `anon_async_api_mixin` with leave actor alive flag
set. Because of `lazy_init` flag actor initialization isn't performed
until message comes, and that message is immediately sent.
CAF should init actor & invoke message processing at least once. Then,
no strong ref to actor is left and it should be auto-destructed by CAF
runtime.

uentity/blue-sky-re,uentity/blue-sky-re,uentity/blue-sky-re