Revert "Import Souncloud tracks uploaded date and tags"

This reverts commit 921a5f941622b8d66e2866d03c405afe233196a4.
Revert created_at date handling for SoundClound favorites imported
tracks because SoundCloud API doesn't provide the date for favorite
action at the moment.
Tracks were imported with it creation date on SoundCloud and not with the
user favorite action date.