Cut throwOnFail

Cut throwOnFail

Summary:
[Folly] Cut `throwOnFail`.

It is not necessary, and `CHECK_THROW`, its reason for existing, can be implemented without it.

It can also easily be a pessimization because there is no way to delay computation of the arguments to the exception ctor until after the check. So if there is, say, a computation using `sformat` to compute a string argument to the exception ctor, that will always be performed rather than being performed only should the check fail.

Reviewed By: Orvid

Differential Revision: D5478804

fbshipit-source-id: 71a125c126eae76c6e95ef1bd23ee883b1db39a5