remove 'demote to pending' task convergence

this effectively added a timeout to container creation, which becomes an
issue in tests, or when downloading docker images.

if the executor disappears, we mark it as failed, which should cover us
if it failed to become running if the executor died hard.

[finishes #76295518]

Signed-off-by: Stew Nickolas <nickolas@us.ibm.com>