os: remove useless if from Wait on unix

Back in the day, Wait used to accept options argument.

CL 4962042 fixed the issue of setting process.done flag when WNOHANG
option was used.

Later, CL 5688046 removed options argument from Wait, but did not remove
pid1 != 0 check which was meant to be used with WNOHANG only.

Remove the check, which is useless and also confusing.

Change-Id: I73b9ef4a0dbe35466e659ca58b896d515ba86d02
Reviewed-on: https://go-review.googlesource.com/c/go/+/543736
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: kolyshkin

src/os/exec_unix.go

@@ -48,9 +48,7 @@ func (p *Process) wait() (ps *ProcessState, err error) {
 	if e != nil {
 		return nil, NewSyscallError("wait", e)
 	}
-	if pid1 != 0 {
-		p.setDone()
-	}
+	p.setDone()
 	ps = &ProcessState{
 		pid:    pid1,
 		status: status,