testsuite: remove EggTestSuite

We no longer run tests with `python setup.py`, but simply with `python -m unittest`

With slapos!862 we no longer need this

See merge request !1316
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:22:57

passed ERP5.PerformanceTest-Master

00:22:51

failed ERP5.UnitTest-Master

02:52:29

failed ERP5.UnitTest-Master.Medusa

02:46:28

passed SlapOS.Eggs.UnitTest-Master.Python2

00:43:21

passed SlapOS.Eggs.UnitTest-Master.Python3

00:11:16