1. Removed an unused public constant
2. Hide PrintFileDocumentAdapter which makes doing the wring
thing easy.
3. We allow a print service to set a tag of a print job which is
an arbitrary string it only knows how to interpret. Typically,
this is the id of a remote print job. This tag was visible to
applications which is wrong - this is data that should be
private to the print service. Now the print service is the
only one to see that.
bug:11084635
Change-Id: I763ea9ff0fdf647805bc36e1737d72263090714d
b450d0d4d7