pycompat: remove large Python 2 block
We no longer support Python 2. So we can delete its compatibility
code and remove the conditional and dedent the Python 3 code.
In order to make the linter happy, we had to inline imports in the
stanza at the top of the file.
Differential Revision: https://phab.mercurial-scm.org/D12250
pager.pager=p0 # $TESTTMP/sysrc:4
ui.editor=e1 # $TESTTMP/userrc:2
pager.pager=p2 # $PAGER
ui.editor=e1 # $TESTTMP/userrc:2