Replace the test_data radical.py

The one formerly in 
  rmgpy/data/test_data/thermo/groups/radical.py
has now been put in 
  test/rmgpy/test_data/testing_database/thermo/groups/radical.py

It is much smaller, and just used for testing if one can remove groups
from a tree during some thermo tests.
test/rmgpy/data/thermoTest.py::TestCyclicThermo::test_remove_group

I don't know what the other was used for, if anything.