Remove very old (and now misleading) design documents.

doc/txt/API.for.DPCS.txt

doc/txt/bgl.txt

doc/txt/job.api.txt

doc/txt/job.initiation.design.txt

doc/txt/job.manager.design.txt

doc/txt/job_data.txt

doc/txt/job_manager_demo.txt

doc/txt/machine.status.demo.txt

doc/txt/machine.status.design.txt

doc/txt/message.summary.txt

doc/txt/misc.issues.txt

doc/txt/partition.demo.txt

doc/txt/partition.design.txt

doc/txt/slurm.protocol.txt