Fixed tests by moving mkdocs/test.py to test.py

If you run Python from inside the mkdocs package, it
doesn’t think mkdocs is a package and relative imports
are an error.

If you run Python from _outside_ the mkdocs package,
then it’s a package and you need relative imports.

test.py isn’t used by anything else in mkdocs, so the
simplest answer seems to be moving it outside the
package.
Fixed flake8 warnings for mkdocs/mkdocs.py

* added a space before “coding: 8tf-8”
* removed an unused shutil import
* removed a blank line before EOF