gopack: simplify go metadata code
gopack: simplify go metadata code

There's only one Go object file per package now,
so there's no need to parse the metadata and merge
metadata from multiple files.  Just save the original
and use it as __.PKGDEF verbatim.

R=r
CC=golang-dev
http://codereview.appspot.com/1647042

h8liu/golang,nightlyone/golang,bdwalton/debian-golang,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,tianon/debian-golang,h8liu/golang,tianon/debian-golang,nightlyone/golang,gnanderson/go,gnanderson/go,ssrl/go,ssrl/go,tianon/debian-golang,nightlyone/golang,dsriram/golang,pombredanne/go-deleteme,ssrl/go,gnanderson/go,tianon/debian-golang,tianon/debian-golang,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,ssrl/go,pombredanne/go-deleteme,nightlyone/golang,pombredanne/go-deleteme,h8liu/golang,h8liu/golang,bdwalton/debian-golang,tv42/old-go,ssrl/go,bdwalton/debian-golang,dsriram/golang,bdwalton/debian-golang,apparentlymart/golang,apparentlymart/golang,dsriram/golang,tv42/old-go,gnanderson/go,h8liu/golang,dsriram/golang,tianon/debian-golang,tv42/old-go,bdwalton/debian-golang,pombredanne/go-deleteme,tianon/debian-golang,ssrl/go,apparentlymart/golang,apparentlymart/golang,bdwalton/debian-golang,h8liu/golang,bdwalton/debian-golang,bdwalton/debian-golang,nightlyone/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,tianon/debian-golang,h8liu/golang,nightlyone/golang,gnanderson/go,dsriram/golang,nightlyone/golang,ssrl/go