No way to delete a field

[mnolletti69]

Issue Description

Normally I deleted unwanted fields clearing the field name and saving.
Now this is not more possible and the schema is messed up.
Struct version: 2025-05-12

Step to reproduce:

• Create a new schema
• Add Test1, Test2, Test3 a new field with default settings
• Clear the Test2 field name (in order to delete them) and save
• Now a warning appears: "Label already exists in schema, second occurance was renamed to 1."
• The Test2 field is not deleted
• A new field with label 1 si added to the schema
• If you save again without changes a new field with label 2 si added to the schema and so on
• If you export the schema, remove the unwanted fields and reimport the schema, the unwanted fields persists
• When the move plugin Move is installed the db related to that schema create a php error in the page
• if you remove the move plugin the error disappears but the schema is messed up