Allow deletion of boards from Set Assignments
Allow deletion of boards from Set Assignments

# The return value of the API call had changed type, from a list to a map
# of lists. The map had a key of the current board, even when the value of
# that key was an empty list; meaning the "length" was never zero.

ucam-cl-dtg/isaac-app,ucam-cl-dtg/isaac-app,ucam-cl-dtg/isaac-app,ucam-cl-dtg/isaac-app