go/printer: simply ignore filename changes in position information
go/printer: simply ignore filename changes in position information

There's no good reason to make any printer state adjustments
simply because the file name in node position information has
changed. Eliminate the relevant code.

R=r
CC=golang-dev
http://codereview.appspot.com/6856054

rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,mhennings/marcohennings-go,rdp/rogerpack2005-golang,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,d0f/go-zh,mhennings/marcohennings-go,scirelli/scirelli-go,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,mhennings/marcohennings-go,bryanxu/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,scirelli/scirelli-go,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,bryanxu/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,rflanagan/reginaldflanagan-project1,webfd/go-zh,bryanxu/go-zh,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,webfd/go-zh,d0f/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,mhennings/marcohennings-go,rdp/rogerpack2005-golang,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,webfd/go-zh,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,mhennings/marcohennings-go,webfd/go-zh,rflanagan/reginaldflanagan-project1,d0f/go-zh,webfd/go-zh,d0f/go-zh,scirelli/scirelli-go,mhennings/marcohennings-go