Make shebang explicit /usr/bin/python2 where it's still there

Both Archlinux and Fedora 29 have guidelines to point explicitly at
/usr/bin/python2 where it expect python2.

Also, do not use env.

Fixes QubesOS/qubes-issues#4027

misc/qubes-desktop-run

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 
 from qubesagent.xdg import launch
 import sys

misc/qubes-session-autostart

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/python2
 # -*- coding: utf-8 -*-
 #
 # The Qubes OS Project, http://www.qubes-os.org

misc/qvm-features-request

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/python2
 # vim: fileencoding=utf-8
 
 #

misc/yum-qubes-hooks.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 #
 # The Qubes OS Project, http://www.qubes-os.org
 #

qubes-rpc/qrun-in-vm

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 # Send the command to the remote side, and then transfer stdin from local to
 # remote and stdout from remote to local.
 #

qubes-rpc/xdg-icon

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 import xdg.IconTheme
 import sys
 import os

qubesagent/xdg.py

@@ -1,5 +1,3 @@
-#!/usr/bin/python
-
 from gi.repository import Gio  # pylint: disable=import-error
 from gi.repository import GLib  # pylint: disable=import-error
 import sys