Issue 5565: simplify python-related makefiles

https://sourceforge.net/p/testlilyissues/issues/5565/

Avoid encoding unnecessary details of Python compilation into the
build rules.  Remove some cruft.

I hope that these changes will work equally well with Python 2 and 3,
but I have only tested in an environment with 2.

[lemzwerg, 2019-10-03 04:27:01]

LGTM.

https://codereview.appspot.com/581080044/diff/578940043/stepmake/stepmake/pyt...
File stepmake/stepmake/python-module-rules.make (right):

https://codereview.appspot.com/581080044/diff/578940043/stepmake/stepmake/pyt...
stepmake/stepmake/python-module-rules.make:1: .DELETE_ON_ERROR:
Looking into the info file of make it seems that DELETE_ON_ERROR has a global
meaning.  If this is true I suggest that you put it into the topmost make file.

[Dan Eble, 2019-10-03 12:02:58]

On 2019/10/03 04:27:01, lemzwerg wrote:
> Looking into the info file of make it seems that DELETE_ON_ERROR has a global
> meaning.  If this is true I suggest that you put it into the topmost make
file.

The thought crossed my mind, but there's a lot I don't yet know about
this build system, and I was worried that that change might impact a
workflow in an area I haven't tested.

It looks like make/stepmake.make is an appropriate place to put it,
near where ".SECONDARY:" appears.  I will try moving it there in a
separate commit and test the python rules again.  If any undesirable
side effects are discovered later, only the second commit will need to
be reverted.

[Dan Eble, 2019-10-03 18:27:18]

move DELETE_ON_ERROR to stepmake.make