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.
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..