hgweb: avoid using `sslutil.modernssl`
`sslutil.modernssl` is going to be removed. Since the point of using this
attribute was to check the importability of the `sslutil`, a different
attribute can be used. `sslutil.wrapserversocket` is used because it’s anyway
used a few lines below.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state