The build instructions are not that interesting, it's a toss-up
between CC0 and BSD-2, but because other CMake bits are BSD-2-Clause,
apply that to more CMakeLists. The copyright date isn't all that
accurate, but these are just inconsequential files.
While here, tidy up and get rid of some useless intermediates.
This is orthogonal to the SKIP_* mechanism already documented
for avoiding modules. If the module is enabled, but its dependencies
are not present, don't bother building the module. This follows
e.g. plasmalnf as an "avoidably heavy dependency".
Related to a misplaced comment in ISSUE #956
