bpo-36384: Leading zeros in IPv4 addresses are no longer tolerated (GH-25099)

Reverts commit e653d4d8e820a7a004ad399530af0135b45db27a and makes
parsing even more strict. Like socket.inet_pton() any leading zero
is now treated as invalid input.

Signed-off-by: Christian Heimes <christian@python.org>

Co-authored-by: Łukasz Langa <lukasz@langa.pl>