add gocritic/ruleguard checks back again, cleanup code. (#13665)

- remove some duplicated code
- reported a bug, separately fixed in #13664
- using strings.ReplaceAll() when needed
- using filepath.ToSlash() use when needed
- remove all non-Go style comments from the codebase

Co-authored-by: Aditya Manthramurthy <donatello@users.noreply.github.com>

cmd/metacache-entries_test.go

@@ -81,6 +81,7 @@ func Test_metaCacheEntries_merge(t *testing.T) {
 	}
 	// Merge b into a
 	a.merge(b, -1)
+	//nolint:gocritic
 	want := append(loadMetacacheSampleNames, loadMetacacheSampleNames...)
 	sort.Strings(want)
 	got := a.entries().names()