Cleanup model/utils.go (#17945)

* Cleanup model/utils.go

- Removed some functions which were unsued. (The unused linter was somehow failing to catch this).
- Moved some functions inside other packages.
- Removed two duplicate instances of the same function - RemoveDuplicateStrings and UniqueStrings.
- Moved some regexes to global vars to prevent compilation every time.

```release-note
NONE
```

* fix lint

```release-note
NONE
```

* bring back unused exception

```release-note
NONE
```

* fix tests

```release-note
NONE
```

* Address review comments

```release-note
NONE
```

api4/role_test.go

@@ -5,6 +5,7 @@ package api4
 
 import (
 	"context"
+	"sort"
 	"strings"
 	"testing"
 
@@ -223,7 +224,9 @@ func TestPatchRole(t *testing.T) {
 		assert.Equal(t, received.Name, role.Name)
 		assert.Equal(t, received.DisplayName, role.DisplayName)
 		assert.Equal(t, received.Description, role.Description)
-		assert.EqualValues(t, received.Permissions, []string{"manage_system", "create_public_channel", "manage_incoming_webhooks", "manage_outgoing_webhooks"})
+		perms := []string{"manage_system", "create_public_channel", "manage_incoming_webhooks", "manage_outgoing_webhooks"}
+		sort.Strings(perms)
+		assert.EqualValues(t, received.Permissions, perms)
 		assert.Equal(t, received.SchemeManaged, role.SchemeManaged)
 
 		// Check a no-op patch succeeds.
@@ -252,7 +255,9 @@ func TestPatchRole(t *testing.T) {
 		assert.Equal(t, received.Name, role.Name)
 		assert.Equal(t, received.DisplayName, role.DisplayName)
 		assert.Equal(t, received.Description, role.Description)
-		assert.EqualValues(t, received.Permissions, []string{"manage_system", "manage_incoming_webhooks", "manage_outgoing_webhooks"})
+		perms := []string{"manage_system", "manage_incoming_webhooks", "manage_outgoing_webhooks"}
+		sort.Strings(perms)
+		assert.EqualValues(t, received.Permissions, perms)
 		assert.Equal(t, received.SchemeManaged, role.SchemeManaged)
 
 		t.Run("Check guest permissions editing without E20 license", func(t *testing.T) {