x/tools: assume go1.22 and simplify

This CL does not include simplifications to gopls.

Updates golang/go#65917
Updates golang/go#69095

Change-Id: I2b54992681e2c671324e22668d8401962a1d2363
Reviewed-on: https://go-review.googlesource.com/c/tools/+/593683
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: adonovan

internal/gocommand/invoke.go

@@ -16,7 +16,6 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
-	"reflect"
 	"regexp"
 	"runtime"
 	"strconv"
@@ -250,16 +249,13 @@ func (i *Invocation) run(ctx context.Context, stdout, stderr io.Writer) error {
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
 
-	// cmd.WaitDelay was added only in go1.20 (see #50436).
-	if waitDelay := reflect.ValueOf(cmd).Elem().FieldByName("WaitDelay"); waitDelay.IsValid() {
-		// https://go.dev/issue/59541: don't wait forever copying stderr
-		// after the command has exited.
-		// After CL 484741 we copy stdout manually, so we we'll stop reading that as
-		// soon as ctx is done. However, we also don't want to wait around forever
-		// for stderr. Give a much-longer-than-reasonable delay and then assume that
-		// something has wedged in the kernel or runtime.
-		waitDelay.Set(reflect.ValueOf(30 * time.Second))
-	}
+	// https://go.dev/issue/59541: don't wait forever copying stderr
+	// after the command has exited.
+	// After CL 484741 we copy stdout manually, so we we'll stop reading that as
+	// soon as ctx is done. However, we also don't want to wait around forever
+	// for stderr. Give a much-longer-than-reasonable delay and then assume that
+	// something has wedged in the kernel or runtime.
+	cmd.WaitDelay = 30 * time.Second
 
 	// The cwd gets resolved to the real path. On Darwin, where
 	// /tmp is a symlink, this breaks anything that expects the