This commit extends the timeout around the `readTChan` in the ping-pong
test to 60 seconds, mostly to account for CI slowness and to rule-out
potential source of flakyness.

The calls to `threadDelay` have been removed, as they doesn't seem to
affect the overall stability of the test (at least locally) -- the
point of the exercise is trying to expose as much as possible potential
problems which might be masked by active waits.