ext4_utils: Yet another MMC discard pain in the ass

Summary:
 * Secure discard on this device is painfully slow. Use regular
   discard until the issue is sorted out.

Test Plan: Needed for devices such as hammerhead

Reviewers: rlasalle15, jriordan001, randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D268