tests/test-issue5979.t

tests: remove obsolete PYTHONPATH override from remotefilelog tests

They were added in
https://bitbucket.org/facebook/hg-experimental/commits/fdcad37a6a68cfbaf5920f3eeaa0cc9cae42bd26,
which says this:

  When remotefilelog moved from its own repo, the tests needed to be updated to
  adjust the PYTHONPATH to ensure the in-repo remotefilelog was loaded instead of
  the system one.

  This meant any local runs of remotefilelog tests would've been using the system
  remotefilelog unless the user had manually set the PYTHONPATH themselves.

That doesn't seem relevant with remotefilelog in core.

Differential Revision: https://phab.mercurial-scm.org/D5248

  $ hg init r1
  $ cd r1
  $ hg ci --config ui.allowemptycommit=true -m c0
  $ hg ci --config ui.allowemptycommit=true -m c1
  $ hg ci --config ui.allowemptycommit=true -m c2
  $ hg co -q 0
  $ hg ci --config ui.allowemptycommit=true -m c3
  created new head
  $ hg co -q 3
  $ hg merge --quiet
  $ hg ci --config ui.allowemptycommit=true -m c4

  $ hg log -G -T'{desc}'
  @    c4
  |\
  | o  c3
  | |
  o |  c2
  | |
  o |  c1
  |/
  o  c0
  

  >>> from mercurial import hg
  >>> from mercurial import ui as uimod
  >>> repo = hg.repository(uimod.ui())
  >>> for anc in repo.changelog.ancestors([4], inclusive=True):
  ...   print(anc)
  4
  3
  2
  1
  0