Remove mxstartup.systemd

mxstartup-systemd.service starts systemd units identified by a
specific filename pattern in /etc/systemd

    mxstartup-HOSTNAME-NAME.service

We decided to get rid of this mechanism and start host specific service
units from /etc/mxstartup instead. The file format of /etc/mxstartup
has been expanded to enable this in #4.

The last units which used this mechanism have been converted [1].

Remove files supporting the obsoleted mechanism.

[1] mariux64/mxtools@c907786

Makefile

@@ -10,10 +10,8 @@ install:
 	mkdir -p -m 0755 ${DESTDIR}${SYSTEMDSYSTEMDIR}
 	install -m 0644 mxstartup-mxvip.service    ${DESTDIR}${SYSTEMDSYSTEMDIR}
 	install -m 0644 mxstartup-classic.service  ${DESTDIR}${SYSTEMDSYSTEMDIR}
-	install -m 0644 mxstartup-systemd.service  ${DESTDIR}${SYSTEMDSYSTEMDIR}
 	mkdir -p -m 0755 ${DESTDIR}${SBINDIR}
 	install -m 0755 mxstartup2mxconfig         ${DESTDIR}${SBINDIR}
 	install -m 0755 mxvipctl                   ${DESTDIR}${SBINDIR}
 	install -m 0755 mxservicectl               ${DESTDIR}${SBINDIR}
 	install -m 0755 mxstartupctl               ${DESTDIR}${SBINDIR}
-	install -m 0755 mxstartup.systemd          ${DESTDIR}${SBINDIR}