HTTP_RAW_POST_DATA is deprecated
You need to edit your php.ini and add or uncomment the following line:

always_populate_raw_post_data = -1


If you've still that error after restarting Apache, you probably edited the wrong file. So as admin, go to Reports/Status/PHP (at /admin/reports/status/php) and double-check your value for always_populate_raw_post_data and your php.ini path.

Note that the above setting will only avoid the warning, see: Changes to PHP-5.6 and this SO post.