Perl core includes a "HTTP::Tiny" module that does what little we need,
and has had it since 5.14 or so, so prefer that instead and remove the
requirement to install libwww-perl.

This also required removing the one minor instance of the URI module,
which is not technically in Perl core but was installed due to LWP.
Instead we just use a regexp 'blessed' by the URI module author.