dtls: remove peer in case of an fatal alert
dtls: remove peer in case of an fatal alert

The logic seams to be wrong here, the peer was removed when it was
*not* deleted from the list of peers, reverse it to fix this problem.

Signed-off-by: Hauke Mehrtens <435ddd46dc66c007a1fa20144c823d37e0d23436@hauke-m.de>

yunus/TinyDTLS-WebID,thecodemaiden/tinydtls-fork,yunus/TinyDTLS-WebID,OlegHahm/tinydtls,jvermillard/tinydtls,nmacs/tinydtls,spark/tinydtls,jvermillard/tinydtls,spark/tinydtls,thecodemaiden/tinydtls-fork,OlegHahm/tinydtls,nmacs/tinydtls,spark/tinydtls,nmacs/tinydtls,fvdnabee/tinydtls,thecodemaiden/tinydtls-fork,fvdnabee/tinydtls,nmacs/tinydtls,yunus/TinyDTLS-WebID,fvdnabee/tinydtls,jvermillard/tinydtls,OlegHahm/tinydtls