Issue Summary

Creating attribute using the Assets External Import marks attribute as unremovable.
The delete attribute action is not available in the Object type Attribute list.

Steps to Reproduce

1. Create a new empty Schema.
2. Create an External Import.
3. Create Object types and attributes using the mapping step.
4. Go to the Attribute list of newly create Object type and try to delete the Attribute

Expected Results

There is an option to delete the attribute

Actual Results

Delete action is not available and all attributes are marked as "removable": false"

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available