Revert "easybuild is a namespace package"

[boegel]

This reverts commit f6f96be (cfr. #1591)

When python setup.py install is used, this error is thrown:

error: Namespace package problem: easybuild is a namespace package, but its
__init__.py does not call declare_namespace()! Please fix it.
(See the setuptools manual under "Namespace Packages" for details.)

[boegel]

The PR tester should have catched this, it'll need to be enhanced.

[hpcugentbot]

EasyBuild framework unit test suite FAILed.

See https://jenkins1.ugent.be/job/easybuild-framework-pr-builder/2629/console for more details.

Please fix the reported issues by pushing additional commits to the branch corresponding with this pull request; contact @boegel if you're not sure what to do.