Build: Remove XSLT option and depend hard on XSLT.
You will now not be able to give --disable-xslt or --enable-xslt
because it is not optional anymore.
https://bugs.webkit.org/show_bug.cgi?id=112368

Patch by Tobias Mueller <tobiasmue@gnome.org> on 2013-03-14
Reviewed by Martin Robinson.

* Source/autotools/FindDependencies.m4:
    Always check for libxslt

* Source/autotools/PrintBuildConfiguration.m4:
    Removed printing out the value of XSLT

* Source/autotools/ReadCommandLineArguments.m4:
    Removed reading XSLT options

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145859 268f45cc-cd09-0410-ab3c-d52691b4dbfc