doc: Disable preface.autolabel in XSLT

The makes the output more consistent with the existing DSSSL setup.

doc/src/sgml/stylesheet-common.xsl

@@ -32,7 +32,6 @@
 <xsl:param name="toc.section.depth">2</xsl:param>
 <xsl:param name="linenumbering.extension" select="'0'"></xsl:param>
 <xsl:param name="generate.index" select="1 - $pg.fast"></xsl:param>
-<xsl:param name="preface.autolabel" select="1 - $pg.fast"></xsl:param>
 <xsl:param name="section.autolabel" select="1 - $pg.fast"></xsl:param>
 <xsl:param name="section.label.includes.component.label" select="1 - $pg.fast"></xsl:param>
 <xsl:param name="refentry.xref.manvolnum" select="0"/>