remove_parent_keep_children.xsl

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0" xmlns:text="www.doc.com">
  <xsl:output method="xml" indent="yes"/>
  <xsl:strip-space elements="*"/>

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
   </xsl:template>

  <xsl:template match="//text:span[@text:style-name='Kursiv_5f_KeiinRecht']">
    <xsl:apply-templates select="node()" />
  </xsl:template>

</xsl:stylesheet>