Revert "internal/build: ignore some files in FindMainPackages (ethereum#27521)"

This reverts commit 5bed0f5.

Author: devopsbo3

internal/build/util.go

@@ -197,9 +197,6 @@ func FindMainPackages(dir string) []string {
 	}
 	for _, cmd := range cmds {
 		pkgdir := filepath.Join(dir, cmd.Name())
-		if !cmd.IsDir() {
-			continue
-		}
 		pkgs, err := parser.ParseDir(token.NewFileSet(), pkgdir, nil, parser.PackageClauseOnly)
 		if err != nil {
 			log.Fatal(err)