Is it possible to remove an assignment from a note? 

No, to maintain our excellent standards of traceability in all projects in BulldozAIR, once a note has been already assigned to a contributor, he or she cannot be removed from the note as allowing this could lead to problematic situations such as:

Collaborators removing themselves from tasks to avoid responsibility on delayed, incomplete or mishandled tasks
Owners removing collaborators from notes to restrain access to information thus, putting collaborators at a disadvantage to answer to the reasons behind this decision