Find docbook-xsl and dblatex templates on Red Hat/Fedora

Remove unused configure checks for dblatex.

Find docbook-xsl and dblatex templates on Red Hat/Fedora: /usr/share/sgml/docbook/xsl-stylesheets and /usr/share/dblatex are places where docbook-style-xsl and, respectively, dblatex packages on Red Hat systems put their XSL templates. Unless we hint this place it has to be added to ./configure manually (--with-docbook-xsl=...): https://src.fedoraproject.org/rpms/bind/blob/master/f/bind.spec#_691.

On Fedora 30:

Before

./configure
...
checking for Docbook-XSL path... auto
checking for html/docbook.xsl... "not found"
checking for xhtml/docbook.xsl... "not found"
checking for manpages/docbook.xsl... "not found"
checking for html/chunk.xsl... "not found"
checking for xhtml/chunk.xsl... "not found"
checking for html/chunktoc.xsl... "not found"
checking for xhtml/chunktoc.xsl... "not found"
checking for html/maketoc.xsl... "not found"
checking for xhtml/maketoc.xsl... "not found"

After:

./configure
...
checking for Docbook-XSL path... auto
checking for html/docbook.xsl... /usr/share/sgml/docbook/xsl-stylesheets/html/docbook.xsl
checking for xhtml/docbook.xsl... /usr/share/sgml/docbook/xsl-stylesheets/xhtml/docbook.xsl
checking for manpages/docbook.xsl... /usr/share/sgml/docbook/xsl-stylesheets/manpages/docbook.xsl
checking for html/chunk.xsl... /usr/share/sgml/docbook/xsl-stylesheets/html/chunk.xsl
checking for xhtml/chunk.xsl... /usr/share/sgml/docbook/xsl-stylesheets/xhtml/chunk.xsl
checking for html/chunktoc.xsl... /usr/share/sgml/docbook/xsl-stylesheets/html/chunktoc.xsl
checking for xhtml/chunktoc.xsl... /usr/share/sgml/docbook/xsl-stylesheets/xhtml/chunktoc.xsl
checking for html/maketoc.xsl... /usr/share/sgml/docbook/xsl-stylesheets/html/maketoc.xsl
checking for xhtml/maketoc.xsl... /usr/share/sgml/docbook/xsl-stylesheets/xhtml/maketoc.xsl