[ContextManager] Remove the put/get free context cycle

The put/get free context cycle in ContextManager::start() (if
continuation stealing is enabled) became unnecessary with
c66551bf ("[Context] Use 'jmp' instead of 'ret' to kickoff the
context").
51 jobs for remove-put-get-free-context-cycle in 27 minutes and 3 seconds (queued for 4 seconds)