Blender Git Loki

Remove Surface modifier when removing force field from object

Summary:
Before this adding Surface type of force field and removing
this field would leave Surface modifier alive in the stack.

This might be really misleading and annoying.

Now removing force field will ensure no modifiers needed for
it are remained in the stack.

This also fixes missing notifier to redraw modifier stack
when changing force field type.

Reviewers: brecht, campbellbarton

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D13