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
diff --git a/include/Makefile.am b/include/Makefile.am
index 27a4090..38ba14c 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -162,7 +162,7 @@
 	$(AM_V_GEN)sed -e's/XX/$*/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