Do not print INTERNALERROR with --pdb

This gets printed by the terminal reporter already, and currently
results in the same error being displayed twice, e.g. when raising an
`Exception` manually from `pytest.debugging.pytest_exception_interact`.

src/_pytest/debugging.py

@@ -109,9 +109,6 @@ class PdbInvoke(object):
         _enter_pdb(node, call.excinfo, report)
 
     def pytest_internalerror(self, excrepr, excinfo):
-        for line in str(excrepr).split("\n"):
-            sys.stderr.write("INTERNALERROR> %s\n" % line)
-            sys.stderr.flush()
         tb = _postmortem_traceback(excinfo)
         post_mortem(tb)