slurm-llnl: Clean up systemd service file names

The "llnl" suffix is fine for the package name (as there is already
a "slurm" package on AUR), but we don't need to go so far as to na-
me the service files with this convention too; after all, the daem-
ons themselves are still just "slurmd" etc.
slurm-llnl: Update service dependencies
slurm-llnl: Clean up the systemd unit files

Massive cleanup and reorganization of systemd unit files:
- slurmdbd absolutely requires mysqld, so it must use
    "Require=mysqld.service" in addition to "After=mysqld.service"
- If a cluster is using slurmdbd, it must start before slurmctld;
    using "Before=slurmctld.service" in the slurmdbd.service is
    sufficient to instruct systemd to put this before slurmctld
- slurmctld absolutely requires munged, so it must use
    "Require=munged.service"
- slurmd is always dependent on slurmctld, and therefore doesn't
    need to state dependencies on network, munge, etc.
- slurmd absolutely requires slurmctld, so it must use
    "Require=slurmctld.service"
slurm-llnl: Clean up systemd unit headers

It's kinda unneccessary to have attribution in here...
slurm-llnl: Don't use sed hack to find slurmstepd

Instead of sed-hacking the source, just use slurmd's -d option to
specify the path to the slurmstepd binary (in /usr/bin, cuz Arch!).