hgweb: drop references to deprecated cgitb
cgitb is going away and gives warnings when importing, and that make tests
fail:
$TESTTMP/hgweb.cgi:5: DeprecationWarning: 'cgitb' is deprecated and slated for removal in Python 3.13
The lack of a "nice" high level error handler is not a huge problem, neither
for users (where it is disabled anyway) or for tests (where we don't use a
browser and the plain tracebacks often are more readable). It is inevitable
that it is going away, and there is no obvious alternative. Remove it and move
on.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}