Remove SConscript used by m4

After discussion with Jim Bosch, we agreed it was probably easier to use
modern smart editors to make bulk changes to Source.h instead of having
someone in the project try to remember the m4 syntax. Also, we hope to make
that header much simpler by removing a bunch of the deprecated code.

These methods were marked deprecated in 2014: we can cleanup the namespace
quite a bit by deleting them, and they don't appear to be used outside the
afw tests.

Increment schema version and add v1 and v2 compatibliity.

Add a v2 test .fits file, to test v2 compatibility, and use it in a test.