BLD: fix odd usage of cython imports, xref (GH8602)
closes #8602 

easy enough, that import should not have been there. we don't import from other pyx files unless its explicity exported (which is in very few cases).

closed via https://github.com/pydata/pandas/commit/d881ba259a98af23f58cd278dce2e32a3e8da05e
