- build against system libnghttp2.so (which upstream bundles/uses
   since 8.x);
 - switch to bundled http_parser due to build failure and make the
   experimental bundled llhttp (claimed to be 2x faster) default.
 - remove binutils-gold from makedepends, it is not needed;
 - remove ca-certificates from makedepends, it seems the run-time
   dependency is enough.