What is the code that says that the United States of America Marshals will not be seen as the military anymore?
The US Marshals (now the US Marshals Service) was -- as described in the Wikipedia article -- created by the Judiciary Act of 1789 during the first term of the US Congress (and also during the first term of office of George Washington as President of the United States). See also this page from the US Marshals Service web site.
The Marshals have never been part of the military, and they claim to be the oldest national law enforcement organization in the US. They are not and never have been part of the US Army or Navy. According to the Wikipedia article linked above:
The Marshals Service is the primary agency for fugitive operations, the protection of officers of the Federal Judiciary, the management of criminal assets, the operation of the United States Federal Witness Protection Program and the Justice Prisoner and Alien Transportation System, and execution of federal arrest warrants. Throughout its history, the Marshals have also provided unique security and enforcement services including protecting African-American students enrolling in the South during the civil rights movement, escort security for United States Air Force LGM-30 Minuteman missile convoys, law enforcement for the United States Antarctic Program, and protection of the Strategic National Stockpile.
The United States Marshals Service, a federal agency, was created in 1969.