This removes a need for packagers to either patch our shebangs or pick
a particular python.
This was already done in __fish_config_interactive (where we need to
duplicate the code because it involves backgrounding).
Work towards #3970.
I hate doing this but I am tired of touching a fish script as part of
some change and having `make style` radically change it. Which makes
editing fish scripts more painful than it needs to be. It is time to do
a wholesale reformatting of these scripts to conform to the documented
style as implemented by the `fish_indent` program.
My previous change to avoid creating a *.pyc file when running
create_manpage_completions.py was wrong because I put the
`sys.dont_write_bytecode = True` on the wrong line. Rather than simply
move that statement make the simpler, cleaner, fix that removes the need
for `eval` where that program is invoked.
