MNT: use plain "python" in hashbang lines

This reverts commit 19d21fb.

Author: pavoljuhas

conda-recipe/run_test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 
 import diffpy.structure.tests
 assert diffpy.structure.tests.test().wasSuccessful()

devutils/makesdist

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 
 '''Create source distribution tar.gz archive, where each file belongs
 to a root user and modification time is set to the git commit time.

devutils/sgtbx_extra_groups.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 
 '''Quick and extremely dirty script for generating code for SpaceGroup that
 are defined in cctbx, but not in mmLib.  It was used to generate module

doc/manual/source/conf.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 # -*- coding: utf-8 -*-
 #
 # diffpy.structure documentation build configuration file, created by

setup.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 
 """Objects for storage and manipulation of crystal structure data.
 

src/diffpy/Structure.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 ##############################################################################
 #
 # diffpy.structure  Complex Modeling Initiative

src/diffpy/structure/__init__.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 ##############################################################################
 #
 # diffpy.structure  by DANSE Diffraction group

src/diffpy/structure/_legacy_importer.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 ##############################################################################
 #
 # diffpy.structure  Complex Modeling Initiative

src/diffpy/structure/applications/__init__.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 ##############################################################################
 #
 # diffpy.structure  by DANSE Diffraction group

src/diffpy/structure/applications/anyeye.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 ##############################################################################
 #
 # diffpy.structure  by DANSE Diffraction group