docs: stop the copyright verbiage from getting included in the POT file

docs: stop the copyright verbiage from getting included in the POT file

For some reason the asciidoc parser from `po4a` includes *all* comments
from an adoc file into the util-linux-man.pot file.  Xgettext had a way
to include only certain comments, but `po4a` does not appear to have a
dedicated mechanism for this.

So... use some bricolage: insert a fruitless 'ifdef' as a barrier
between the copyright/license comment and the title line.  This
prevents `po4a` from seeing the two things as belonging together.

This shrinks the util-linux-man.pot file by 1267 lines (2.5%),
equivalent to nearly 67kB (4.8%).

Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>