Fix unidiomatic type checking

common/lib/capa/capa/inputtypes.py

common/lib/capa/capa/responsetypes.py

common/lib/capa/capa/tests/response_xml_factory.py

common/lib/chem/chem/chemcalc.py

common/lib/symmath/symmath/formula.py

common/lib/symmath/symmath/symmath_check.py

common/lib/xmodule/xmodule/lti_2_util.py

common/lib/xmodule/xmodule/tabs.py

lms/djangoapps/foldit/tests.py

lms/djangoapps/lms_migration/migrate.py

lms/djangoapps/mobile_api/social_facebook/courses/views.py

lms/djangoapps/mobile_api/social_facebook/friends/views.py

lms/djangoapps/notes/models.py