pix_url deprecated but still in use for Moodle 3.3 version

[logan-reynolds]

When testing 3.3.0 (build 2017090600) from Moodle.org on Totara 12 (which is based on Moodle 3.3), the following error is encountered which indicates pix_url occurrences need updated to either image_url or pix_icon as appropriate:

pix_url is deprecated. Use image_url for images and pix_icon for icons.

    line 2021 of /lib/setuplib.php: call to debugging()
    line 77 of /blocks/use_stats/renderer.php: call to renderer_base->pix_url()
    line 186 of /blocks/use_stats/block_use_stats.php: call to block_use_stats_renderer->per_course()
    line 340 of /blocks/moodleblock.class.php: call to block_use_stats->get_content()
    line 266 of /blocks/moodleblock.class.php: call to block_base->formatted_contents()
    line 1247 of /lib/blocklib.php: call to block_base->get_content_for_output()
    line 1302 of /lib/blocklib.php: call to block_manager->create_block_contents()
    line 281 of /lib/outputrenderers.php: call to block_manager->ensure_content_created()
    line 37 of /theme/basis/layout/partials/head.php: call to core_renderer->standard_head_html()
    line 39 of /theme/basis/layout/default.php: call to require()
    line 898 of /lib/outputrenderers.php: call to include()
    line 828 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
    line 252 of /course/view.php: call to core_renderer->header()