Allow deleting custom task type

### Description of the issue
I could not delete a custom task type even though no issue was referencing it.

### Your environment
* Version of Huly: 0.6.343 (0.6.343)
* Browser (and version): Huly Desktop
* Your operating system (and version): MacOS Sequoia 15.1

### Steps to reproduce
1) Create a custom task type in Classic Project space settings
2) Try and delete it.

### Expected behaviour
The custom task type should be able to be deleted when no issues are referencing it.

### Actual behaviour
The custom task type is not able to be deleted. Even if so, there's no deletion UI for it.