MAINT: lib: Clean up in twodim_base.py.
MAINT: lib: Clean up in twodim_base.py.

* Remove unused imports.

madphysicist/numpy,rgommers/numpy,pbrod/numpy,anntzer/numpy,rgommers/numpy,anntzer/numpy,endolith/numpy,WarrenWeckesser/numpy,rgommers/numpy,jakirkham/numpy,pbrod/numpy,abalkin/numpy,mhvk/numpy,mhvk/numpy,seberg/numpy,abalkin/numpy,seberg/numpy,simongibbons/numpy,charris/numpy,mattip/numpy,grlee77/numpy,grlee77/numpy,simongibbons/numpy,anntzer/numpy,endolith/numpy,madphysicist/numpy,WarrenWeckesser/numpy,endolith/numpy,endolith/numpy,grlee77/numpy,pdebuyl/numpy,jakirkham/numpy,mattip/numpy,mhvk/numpy,grlee77/numpy,anntzer/numpy,charris/numpy,numpy/numpy,WarrenWeckesser/numpy,numpy/numpy,charris/numpy,abalkin/numpy,pbrod/numpy,mhvk/numpy,jakirkham/numpy,madphysicist/numpy,mhvk/numpy,rgommers/numpy,simongibbons/numpy,mattip/numpy,charris/numpy,WarrenWeckesser/numpy,mattip/numpy,jakirkham/numpy,simongibbons/numpy,pdebuyl/numpy,simongibbons/numpy,numpy/numpy,numpy/numpy,grlee77/numpy,madphysicist/numpy,madphysicist/numpy,pdebuyl/numpy,pbrod/numpy,pdebuyl/numpy,WarrenWeckesser/numpy,seberg/numpy,pbrod/numpy,seberg/numpy,jakirkham/numpy