Remove old workaround for F5

Remove old workaround for F5

F5 is well-known for needing workaround (go read RFC 8446). In this
particular case, it required implementation sending CHs larger than
255 bytes to 0x0300 otherwise their server would hang. This is the
same hang that required the CH padding extension which broke other
implementations. The CH padding extension was removed ~6 years ago,
so hopefully this kludge will no longer needed either.

ok jsing