Remove required clause on Projects::CustomFields

It is not necessary anymore, because the required fields are already returned in the project mapping clause, because required custom fields
also have a read-only mapping created.

app/models/projects/custom_fields.rb

@@ -42,7 +42,6 @@ def available_custom_fields
       return all_visible_custom_fields if new_record?
 
       all_visible_custom_fields.where(id: project_custom_field_project_mappings.select(:custom_field_id))
-                               .or(required_visible_custom_fields)
     end
 
     # Note:
@@ -64,10 +63,6 @@ def all_visible_custom_fields
       all_available_custom_fields.visible(project: self)
     end
 
-    def required_visible_custom_fields
-      ProjectCustomField.required.visible(project: self)
-    end
-
     def custom_field_values_to_validate
       # Limit the set of available custom fields when the validation is limited to a section
       if _limit_custom_fields_validation_to_section_id