Clean up backend Makefile.am files

Moved all backend *.h files into the SOURCES primary as Automake
documentation states all source file types should be listed.  This
causes Automake to include *.h files in rebuild rules for the targets.

Removed the '-DIN_HAMLIB' assignment from the CFLAGS primary in each
backend and assigned it to AM_CPPFLAGS in configure.ac.  The effect is
the same and it simplifies the backend Makefile.am files.

Removed all commented lines.