systemd-sysv-install: change license to MIT-0

See parent commit for explanation.

git blame shows Martin Pitt is the author of the code.

(I was considering whether we should instead drop this file, but it's still
useful for *distributions*. Eveen if we discourage people from using sysv
scripts, distributions will have to deal with them for a while yet.)

src/systemctl/systemd-sysv-install.SKELETON

@@ -1,5 +1,5 @@
 #!/bin/sh
-# SPDX-License-Identifier: CC0-1.0
+# SPDX-License-Identifier: MIT-0
 #
 # This script is called by "systemctl enable/disable" when the given unit is a
 # SysV init.d script. It needs to call the distribution's mechanism for