core: move packages used to build man page from "Build-Depends-Indep" to "Build-Depends" (debian packaging)

Packages asciidoc, source-highlight, xsltproc, docbook-xml and docbook-xsl are
now used to build man page in the package weechat-curses, which is not
arch-independent.
So these dependencies are moved from "Build-Depends-Indep" to "Build-Depends".