Fix to thermoTest TestCyclicThermo::test_remove_group

The test depends on the radical groups tree in the testing 
database being a certain way, which it no longer is.
We used to test it on a different dummy database, which we have
just removed to reduce redundancy, but rather than change the database
to be that way (which messes up other tests) I am modifying the test 
to first put the database (in memory) the way it expects it to be.

The function being tested here (remove_group) is never used in RMG.
It was written in 89901fa 
by nyee who wrote, in 2016, "Currently, I am using this to remove CS groups as they 
are not detected properly". So we're fixing a broken test for a working
function that is never used.

Author: rwest

test/rmgpy/data/thermoTest.py

@@ -1644,6 +1644,9 @@ def test_remove_group(self):
         group_to_remove = rad_group.entries["RJ"]
         children = group_to_remove.children
 
+        # set up for testing below
+        rad_group.entries["OJ"].data = "RJ"
+
         # remove the group
         rad_group.remove_group(group_to_remove)
 
@@ -1663,6 +1666,7 @@ def test_remove_group(self):
 
         # if group_to_remove is a pointer and another node pointed to it, we copy
         # group_to_remove pointer
+        # OJ pointed to RJ and RJ pointed to CJ so if you remove RJ then OJ should point to CJ
         assert rad_group.entries["OJ"].data is group_to_remove.data
 
         # Remove an entry with a ThermoData object