Remove execution-time which can vary from machine to machine.

@luke , As we discussed. Merging dierctly.

Tests passing in
https://nexedi.erp5.net/test_result_module/20200117-9F5C0733

/reviewed-on !181
2 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-Master.Python2

00:51:49

passed SlapOS.Eggs.UnitTest-Master.Python3

00:18:33