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/iam-store.go

@@ -171,7 +171,7 @@ func newMappedPolicy(policy string) MappedPolicy {
 
 // key options
 type options struct {
-	ttl int64 //expiry in seconds
+	ttl int64 // expiry in seconds
 }
 
 type iamWatchEvent struct {
@@ -558,9 +558,7 @@ func (store *IAMStoreSys) AddUsersToGroup(ctx context.Context, group string, mem
 		// exist.
 		gi = newGroupInfo(members)
 	} else {
-		mergedMembers := append(gi.Members, members...)
-		uniqMembers := set.CreateStringSet(mergedMembers...).ToSlice()
-		gi.Members = uniqMembers
+		gi.Members = set.CreateStringSet(append(gi.Members, members...)...).ToSlice()
 	}
 
 	if err := store.saveGroupInfo(ctx, group, gi); err != nil {