build: Drop data-to-c.pl in favour of data-to-c.py

The Python version was added for the Meson build, but we might as well
use it from autotools too, since it does exactly the same thing as the
Perl version (modulo not including a trailing linebreak, but that
doesn’t matter).

Works fine with Python 2.7 or Python 3.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://bugzilla.gnome.org/show_bug.cgi?id=790147

gio/data-to-c.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 
 import sys