@NonNull
    static Single<Boolean> removeFromFavorites(@NonNull final Geocache cache) {
        return changeFavorite(cache, false);
    }
Removes the cache from the favorites.
<br>
This must not be called from the UI thread.

@param cache the cache to remove
@return {@code false} if an error occurred, {@code true} otherwise
main/src/main/java/cgeo/geocaching/connector/gc/GCParser.java