Facebook had been fighting the government on the legality of the NDOs and lost the initial ruling, but a DC appeals court set a date for a public hearing -- which was scheduled for tomorrow, September 14th. The prosecution's retraction today of the NDO requirement doesn't actually concede the legal arguments brought up jointly by Facebook and the civil and digital rights groups, according to Buzzfeed. The filing just noted that the investigation "progressed ... to the point where the [NDOs] are no longer needed."
The joint filing by Facebook and the US attorney's office in Washington revealed that a lower court judge had vacated the NDO requirements, which made Facebook's appeal unnecessary. Ergo, lawyers are asking the DC appeals court to dismiss the case.
9-13-17 Motion to Dismiss Appeal Facebook by zmtillman on Scribd