pkg/environment: Remove exec related functions

This commit starts the migration to remove the environment package. It
introduced an abstraction that is not being used, and removing it makes
the code simpler to maintain.

This commit removes all 'exec' related package.

pkg/environment/globals.go

@@ -1,12 +1,10 @@
 package environment
 
 import (
-	"context"
 	"io"
 	"io/fs"
 	"os"
 
-	"github.com/tkw1536/goprogram/stream"
 	"github.com/tkw1536/pkglib/pools"
 )
 
@@ -70,8 +68,3 @@ func ReadFile(env Environment, path string) ([]byte, error) {
 	// return the buffer contents!
 	return buffer.Bytes(), nil
 }
-
-// MustExec is like Exec, except that it returns true if the command exited successfully, and else false.
-func MustExec(ctx context.Context, env Environment, io stream.IOStream, workdir string, exe string, argv ...string) bool {
-	return env.Exec(ctx, io, workdir, exe, argv...)() == 0
-}