`xml-editor`: Cannot remove prep type items or add new ones

[grantfitzsimmons]

Screen.Recording.2023-10-23.at.8.44.37.PM.mov

nbm-mnb database copy, /specify/view/picklist/51/

[CarolineDenis]

NOTES:
The issue is not really that we cannot add or delete a prep type, it's the fact that the + and - buttons are enabled and shouldn't.
See comment: #3441 (comment)
This feature will be read only until #3125 is implemented

[CarolineDenis]

Will add back the read only