Fix file deletion on W-03 cards

[alexdu]

My card is a 8GB W-03 (VERSION=FA9CAW3AW3.00.00).

Without this fix, deleting a file locally would attempt to delete it from a card, without success, then it would copy the file back from the card. It looks like the newer firmware doesn't like the __DUMMY__ parameter.

Luckily, the ?& combination is accepted, so the fix was easy.

Additionally, this PR outputs the result of the deletion command (SUCCESS or NG), for easier troubleshooting.