[Scripts] Remove coroutine polls again
[Scripts] Remove coroutine polls again

Polls were meant to back an inheritance-based approach to child
process waiting (i.e., some ProcessExecutor would also wait() for
children along with executing other polls); however, the feature
was implemented as a module-level function instead to better
express that signal handlers are global state.

This (mostly) reverts commit d160c389499c3ca2113c6c9d12e0560d9f0ac88d.

CylonicRaider/Instant,CylonicRaider/Instant,CylonicRaider/Instant,CylonicRaider/Instant,CylonicRaider/Instant