Revert "cmd/sketch: add a process reaper"

The reaper was too fast, and it was reaping processes
that we started with os/exec before os/exec could Wait
on them, which caused Wait to return an error.

Most of our error handling for Wait causes bad things to happen:
sketch exits, diffs look scary, etc.

Revert now, and I'll resubmit later when it's more robust.

This reverts commit 587b57dce0d2301e5628ed3d39e62f20d58d7f48.
diff --git a/cmd/sketch/main.go b/cmd/sketch/main.go
index 6013cba..210db71 100644
--- a/cmd/sketch/main.go
+++ b/cmd/sketch/main.go
@@ -615,14 +615,6 @@
 		os.Setenv("SKETCH_PUB_KEY", pubKey)
 	}
 
-	if inInsideSketch {
-		// Start a process reaper, because we are PID 1.
-		err := startReaper(context.WithoutCancel(ctx))
-		if err != nil {
-			slog.WarnContext(ctx, "failed to start process reaper", "error", err)
-		}
-	}
-
 	wd, err := os.Getwd()
 	if err != nil {
 		return err
diff --git a/cmd/sketch/reaper_linux.go b/cmd/sketch/reaper_linux.go
deleted file mode 100644
index 602deb6..0000000
--- a/cmd/sketch/reaper_linux.go
+++ /dev/null
@@ -1,45 +0,0 @@
-//go:build linux
-
-package main
-
-import (
-	"context"
-	"log/slog"
-	"os"
-	"os/signal"
-
-	"golang.org/x/sys/unix"
-)
-
-func startReaper(ctx context.Context) error {
-	if err := unix.Prctl(unix.PR_SET_CHILD_SUBREAPER, 1, 0, 0, 0); err != nil {
-		return err
-	}
-	go reapZombies(ctx)
-	return nil
-}
-
-// reapZombies runs until ctx is cancelled.
-func reapZombies(ctx context.Context) {
-	sig := make(chan os.Signal, 16)
-	signal.Notify(sig, unix.SIGCHLD)
-
-	for range sig {
-	Reap:
-		for {
-			var status unix.WaitStatus
-			pid, err := unix.Wait4(-1, &status, unix.WNOHANG, nil)
-			switch {
-			case pid > 0:
-				slog.DebugContext(ctx, "reaper ran", "pid", pid, "exit", status.ExitStatus())
-			case err == unix.EINTR:
-				// interrupted: fall through to retry
-			case err == unix.ECHILD || pid == 0:
-				break Reap // no more ready children; wait for next SIGCHLD
-			default:
-				slog.WarnContext(ctx, "wait4 error", "error", err)
-				break Reap
-			}
-		}
-	}
-}
diff --git a/cmd/sketch/reaper_other.go b/cmd/sketch/reaper_other.go
deleted file mode 100644
index 6b03d75..0000000
--- a/cmd/sketch/reaper_other.go
+++ /dev/null
@@ -1,9 +0,0 @@
-//go:build !linux
-
-package main
-
-import "context"
-
-func startReaper(_ context.Context) error {
-	return nil
-}