INT 21,13 - Delete File Using FCB

	AH = 13h
	DS:DX = pointer to an unopened FCB

	on return:
	AL = 00 if file deleted
	   = FF if file not found

	- deletes unopened file with normal attributes
	- FCB must contain drive id, filename, and extension before call
	- "?" wildcard supported after DOS 2.1, "*" supported by DOS 3.x+
	- DOS 2.x allowed deletion of a subdirectory if XFCB was provided,
	  even if files existed, causing lost clusters.  DOS 3.x does not