Remove shebang lines from generated pelicanconf.py and publishconf.py.

These configuration files do not need a #! line as they are not intended to be
executed directly and are not marked as executable. (In practise this doesn't
cause any problems - it just came up in a Guix bug report because Guix
transforms the #! lines.)

The "coding: utf-8" lines are also no longer required now that Pelican is Python
3 only.

pelican/tools/templates/pelicanconf.py.jinja2

@@ -1,6 +1,3 @@
-#!/usr/bin/env python
-# -*- coding: utf-8 -*- #
-
 AUTHOR = {{author}}
 SITENAME = {{sitename}}
 SITEURL = ''

pelican/tools/templates/publishconf.py.jinja2

@@ -1,6 +1,3 @@
-#!/usr/bin/env python
-# -*- coding: utf-8 -*- #
-
 # This file is only used if you use `make publish` or
 # explicitly specify it as your config file.