QUIC: removed check for packet size beyond MAX_UDP_PAYLOAD_SIZE.

QUIC: removed check for packet size beyond MAX_UDP_PAYLOAD_SIZE.

The check tested the total size of a packet header and unprotected packet
payload, which doesn't include the packet number length and expansion of
the packet protection AEAD.  If the packet was corrupted, it could cause
false triggering of the condition due to unsigned type underflow leading
to a connection error.

Existing checks for the QUIC header and protected packet payload lengths
should be enough.