settings: Remove no more needed top level guards

Remove top level guards in settings modules introduced in rDWAPPS0bc0934bca8ee36bcb1e2f8ef57c951fd5c6acca
needed at the time to fix Debian packaging.
After updating debian/rules by specifying the path of the tests to run,
there is no more side effects due to nose importing all swh-web modules
when searching for tests.