useless-if-before-free: fix typo in --help and make the internal,

useless-if-before-free: fix typo in --help and make the internal,

automatic version date update process work once again.
--help output contained a NUL character instead of the
backslash-zero that was intended.  Also, the "must lie within
the first 8 lines" line is on line 9, and hence not getting
automatically updated.
* build-aux/useless-if-before-free: Fix the former by adding a
backslash, and the latter by condensing the three lines of what-it-does
to a single line, leaving one line of slack for the future.