Don't enforce Python 2 for utilities

The conv_gen.py utility was tested against both Python 2 and 3,
so there is no need to enforce Python 2. Also, having:

  #!/usr/local/bin/python{2|3}

is a bad idea, because Python may be installed in a different location.

Change-Id: I6007d481047b584db13d6eda70fb99f11f9ddaa1

include/Makefile.am

@@ -162,7 +162,7 @@ osmocom/core/crc%gen.h: osmocom/core/crcXXgen.h.tpl
 	$(AM_V_GEN)sed -e's/XX/$*/g' $< > $@
 
 osmocom/gsm/gsm0503.h: $(top_srcdir)/utils/conv_gen.py $(top_srcdir)/utils/conv_codes_gsm.py
-	$(AM_V_GEN)python2 $(top_srcdir)/utils/conv_gen.py gen_header gsm \
+	$(AM_V_GEN)python $(top_srcdir)/utils/conv_gen.py gen_header gsm \
 		--target-path $(builddir)/osmocom/gsm
 
 CLEANFILES = osmocom/gsm/gsm0503.h

src/gsm/Makefile.am

@@ -47,6 +47,6 @@ EXTRA_DIST = libosmogsm.map
 
 # Convolutional codes generation
 gsm0503_conv.c: $(top_srcdir)/utils/conv_gen.py $(top_srcdir)/utils/conv_codes_gsm.py
-	$(AM_V_GEN)python2 $(top_srcdir)/utils/conv_gen.py gen_codes gsm
+	$(AM_V_GEN)python $(top_srcdir)/utils/conv_gen.py gen_codes gsm
 
 CLEANFILES = gsm0503_conv.c

tests/Makefile.am

@@ -280,5 +280,5 @@ $(TESTSUITE): $(srcdir)/testsuite.at $(srcdir)/package.m4
 	mv $@.tmp $@
 
 conv/gsm0503_test_vectors.c: $(top_srcdir)/utils/conv_gen.py $(top_srcdir)/utils/conv_codes_gsm.py
-	$(AM_V_GEN)python2 $(top_srcdir)/utils/conv_gen.py gen_vectors gsm \
+	$(AM_V_GEN)python $(top_srcdir)/utils/conv_gen.py gen_vectors gsm \
 		--target-path $(builddir)/conv

utils/conv_codes_gsm.py

@@ -1,5 +1,6 @@
-#!/usr/bin/python2
+#!/usr/bin/env python
 # -*- coding: utf-8 -*-
+
 from conv_gen import ConvolutionalCode
 from conv_gen import poly
 

utils/conv_gen.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/env python
 
 mod_license = """
 /*