Drop deprecated GRMLBASE/48-tmpfs file, use default /tmp handling

Drop deprecated GRMLBASE/48-tmpfs file, use default /tmp handling

The configuration needs to take place in /etc/default/tmpfs
anyway (not /etc/default/rcS) and defaulted to "no". systemd
has a separate tmp.mount unit and quoting systemd changelog:

| systemd (220-6) unstable; urgency=medium
|
|    * Stop installing tmp.mount by default; there are still situations where it
|      becomes active through dependencies from other units, which is surprising,
|      hides existing data in /tmp during runtime, and it isn't safe to have a
|      tmpfs /tmp on every install scenario. (Closes: #783509)
|      - d/rules: Ship tmp.mount in /usr/share/systemd/ instead of
|        /lib/systemd/systemd.
|      - systemd.postinst: When tmp.mount already was enabled, install tmp.mount
|        into /etc and keep it enabled.
|      - systemd.postinst: When enabling tmp.mount because of RAMTMP=yes, copy it
|        from /usr/share.
|      - Drop Don-t-mount-tmp-as-tmpfs-by-default.patch and
|        PrivateTmp-shouldn-t-require-tmpfs.patch, not necessary any more.