Discard the 'master' makefile, in favour of using Automake for all

builds of agedu. Building the man page from the .but file is included
in the Automake makefile, but omitted if configure can't find halibut,
in which case 'make clean' also won't destroy the now-non-rebuildable
agedu.1.

git-svn-id: svn://svn.tartarus.org/sgt/agedu@9245 cda61777-01e9-0310-a592-d414129be87e