BlankLineStrippingWriter: clean up the code.

Writing to buffer always returns without error.
Remove unreachable return:
	go vet .
	util.go:80: unreachable code
I think it's not misbehaving, it's just ignored. By writing into a buffer it is expected the same value as len([]byte) you are writing. See readAll http://golang.org/src/pkg/io/ioutil/ioutil.go?s=1147:1188#L31