files: drop extra history push on source pages that trapped the user without option for going back (Issue #343) Source pages don't need any special history awareness.

pytest >= 3.3.0, < 3.8
pytest-runner < 4.3
pytest-sugar >= 0.7.0, < 0.10
pytest-benchmark < 3.2
pytest-localserver < 0.5
mock < 2.1
Sphinx < 1.8
WebTest < 2.1