packaging: remove py2exe / Python 2.7 support
This commit started by deleting references to py2exe (which is only used
on Python 2). After pulling the thread, quite a lot of code was orphaned
and was deleted.
Differential Revision: https://phab.mercurial-scm.org/D12265
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true