dumpBackup.php: Remove --force-normal option

dumpBackup.php: Remove --force-normal option

The code handling this option, added in r14151 / 64cbfd80b576, used to call
dl() to allow use of the utfnormal library's custom PHP extension even if
it is not enabled in php.ini. That part was removed in 1.22 (d0c8ba037cf6).

And as pointed out by Ariel Glenn[1], the utfnormal library later dropped
support for that PHP extension in 6c61fd7c7843 (in favor of intl, which had
already been supported since 1.17 (r69626 / f08147c313f5)), so there is now
no reason whatsoever to check for utf8_normalize(). The option will now be
treated like any other unrecognized option and will be silently ignored.

[1]: https://phabricator.wikimedia.org/T94277#1680209

Change-Id: I467bf609fda6e923fd2d654400d8e1b6c3714d96