undefine

[Dirk Herrmann]

Hi folks,

it seemed that there is consensus that there should not be a possibility
to remove a once existing binding from a module (except by creating a new
empty module and reloading all the other stuff into that).

Thus, I'd like to suggest that we deprecate undefine and its C-level
counterpart scm_m_undefine.

Best regards, 
Dirk Herrmann