fix obvious pylint errors and warnings

.pylintrc-local.yml

examples/curve-pot.py

sumpy/codegen.py

sumpy/e2e.py

sumpy/e2p.py

sumpy/expansion/level_to_order.py

sumpy/kernel.py

sumpy/p2e.py

sumpy/p2p.py

sumpy/point_calculus.py

sumpy/qbx.py

sumpy/symbolic.py

sumpy/tools.py

sumpy/toys.py

sumpy/visualization.py