Revert "test_tools_smoke.py: mayFail test_offwaketime"

This reverts commit be735b0.

Once we are running tests using python3 and the right mode (utf-8), those
test won't be failing with the encoding error like they did earlier on.

tests/python/test_tools_smoke.py

@@ -265,7 +265,6 @@ def test_offcputime(self):
  self.run_with_duration("offcputime.py 1")
 
  @skipUnless(kernel_version_ge(4,6), "requires kernel >= 4.6")
- @mayFail("This fails on ubuntu 18.04 github actions environment")
  def test_offwaketime(self):
  self.run_with_duration("offwaketime.py 1")