Revert "Refactor childStats requestRestartPermission algorithm"

[HCanber]

Reverts #689

PR #689 has altered the algorithm. Unfortunately it introduced several bugs, and needs to be reverted, as support for negative values have been completely removed.

The values for maxNrOfRetries and withinTimeMilliseconds are specified when creating AllForOneStrategy and OneForOneStrategy. From the docs for these constructors:
-- maxNrOfRetries: the number of times a child actor is allowed to be restarted, negative value means no limit, if the limit is exceeded the child actor is stopped.
-- withinTimeMilliseconds: duration in milliseconds of the time window for maxNrOfRetries, negative values means no window.
#689 made these calls do the incorrect thing:

RequestRestartPermission(-1,-1)
RequestRestartPermission(10,-1)
RequestRestartPermission(-1, 10)