Remove superfluous static firstTime checks

There are two changes here:
* The initHookRegistrar was being run when initially when require registers
  itself. But this is just telling it to run `fillModuleListRecord` later,
  which seems cleaner to do as a part of registering require instead of
  indirectly. Note that the debug check can never actually happen as the
  variable `requireDebug` will always be 0 at this point in time.
* The environment variables being set is slightly different, in the sense
  that if you did not `require foo` at all you did not set these environment
  variables at all. However, it seems to me to make more sense to either set
  them independent of loading a module, or perhaps not at all; either which
  way it seems odd that it depended on us loading a module.