Remove the overload of `PullableReader::PullBehindScratch()` with no parameters, which is no longer overridden anywhere.
Remove the overload of `PullableReader::PullBehindScratch()` with no parameters,
which is no longer overridden anywhere.

PiperOrigin-RevId: 439554109

google/riegeli,google/riegeli,google/riegeli,google/riegeli