[otbn,dv] Remove unused import from RIG's config.py
[otbn,dv] Remove unused import from RIG's config.py

I seem to have added it mistakenly in fddf0d0 in January(!). Oops.

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan