Remove leftover usage of HTTP/Request

[onli]

Some Spartacus plugins still depend on HTTP/Request.php, despite that bundled lib having been removed in 6052932 (I'm not remembering whether there was a discussion about this and do not see a PR, but the justification was likely HTTP/Request.php not working under any current PHP version). Those plugins should be moved to HTTP/Request2 or (better) use serendipity_request_url.

This is likely also a good opportunity to fix or remove broken plugins.

Plugin list:

• 1. serendipity_plugin_piwik
• 2. serendipity_plugin_ggopis
• 3. serendipity_plugin_flickrbadge
• 4. serendipity_event_podcast
• 5. serendipity_event_mobile_output
• 6. serendipity_event_geotag
• 7. serendipity_event_commentspice
• 8. serendipity_event_aggregator
• 9. serendipity_plugin_twitter
• 10. serendipity_plugin_imagesidebar
• 11. serendipity_plugin_gallery_menalto_random
• 12. serendipity_event_recaptcha
• 13. serendipity_event_geourl
• 14. serendipity_event_facebook
• 15. serendipity_event_amazonchooser