Remove useless variable assignments in util.opener.
The original idea might have been to prevent circular references, but
as this assignment would have created another reference, this makes
no difference.
Backed out changeset
cfa477946181824f4c769580ebf59710090ba08a
Only printenv was changed, not the actual execution of hooks.
And not setting an empty value might cause problems on platforms
which can't always remove variables from the environment.