remove redundant condtion

We already know that radicals is True since the preceding line
returned if `not radicals` was True.
remove redundant code and fix typo

The check for the function being zero is part of the standard
'free_symbols' and need not be repeated for the specialized
form of the routine in `_free_symbols`.
Merge pull request #7405 from smichr/polys

remove redundant condtion