cmd/cgo: omit //line in -godefs, -cdefs output
cmd/cgo: omit //line in -godefs, -cdefs output

Makes files like src/pkg/syscall/ztypes_linux_amd64.go easier to read.
(The copy that is checked in predates the //line output mode,
so this also preserves the status quo.)

R=golang-dev, iant, gri
CC=golang-dev
http://codereview.appspot.com/5655068

pombredanne/go-deleteme,gnanderson/go,gnanderson/go,tv42/old-go,gnanderson/go,apparentlymart/golang,gnanderson/go,apparentlymart/golang,apparentlymart/golang,dsriram/golang,gnanderson/go,apparentlymart/golang,tv42/old-go,dsriram/golang,tv42/old-go,apparentlymart/golang,apparentlymart/golang,dsriram/golang,dsriram/golang,dsriram/golang,tv42/old-go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme