backout deprecation of value returned from suite; closes #3744 - #3759

Coverage decreased (-0.009%) to 91.719% when pulling 389597f on boneskull/issue/3744 into 7926f47 on master.

Consider an alternative version, using something like

function isAsync(fn) {
   return fn.constructor.name === 'AsyncFunction';
}

on the describe's function and issuing the deprecation warning based on that.

Or steal Node-10.x's util.types.isAsyncFunction...
See also https://stackoverflow.com/questions/38508420/how-to-know-if-a-function-is-async

@plroebuck we can revisit after this patch release. I would like to just solve async suites.