ChannelZ is a debugging feature in grpc. It has not had appengine support; this commit
removes its support for 1.6, too. This change is because in a recent sys/unix commit
1.6 support was broken.
Reverts grpc/grpc-go#2098
Appengine will fail with the error below:
```
go-app-builder: Failed parsing input: parser: bad import "syscall" in google.golang.org/grpc/channelz/funcs.go from GOPATH
```
The root cause of it is in type_linux.go.
629f6bc5e5/channelz/types_linux.go (L21-L25)
Doug Fawley