Remove ∘ jot dfn global assignment exploit

[rikedyp]

https://course.dyalog.com/Ufns/#name-scope-locals-and-globals

var∘←'lexical'⍵ is an exploit of an implementation edge condition, and not theoretically correct behaviour of dfns. Although people may use this, it should not be encouraged and certainly not demonstrated in an introductory text like this

[mkromberg]

Amen