feat(objectionary#834): simplify vars-float-down

src/main/resources/org/eolang/parser/vars-float-down.xsl

@@ -55,13 +55,7 @@ SOFTWARE.
       <xsl:apply-templates select="node()|@*"/>
     </xsl:copy>
   </xsl:template>
-  <xsl:template match="o[@ref]">
-    <xsl:apply-templates select="." mode="non-empty-ref"/>
-  </xsl:template>
-  <xsl:template match="o[@ref!='']" mode="non-empty-ref">
-    <xsl:apply-templates select="." mode="without-top-ref"/>
-  </xsl:template>
-  <xsl:template match="o[not(ancestor::o[@ref])]" mode="without-top-ref">
+  <xsl:template match="o[@ref and @ref!='' and not(ancestor::o[@ref])]">
     <xsl:variable name="reference" select="@ref"/>
     <xsl:variable name="found" select="key('o-by-line', $reference)"/>
     <xsl:element name="o">