Delete suppressWarning in OSS (#30312)

I'm pretty sure this is completely unnecessary even in www and RN
because it's only useful if you use the mock scheduler which typically
only we do in our own tests. But all our tests pass so unless www/RN
does something with it, I don't think this is used.

Also remove unnecessary `__DEV__` check. If it gets pulled in prod, we'd
want to know about it.