remove all trailing blank lines

by running this command:
git ls-files -z | xargs -0 perl -pi -0777 -e 's/\n\n+$/\n/'
This is in preparation for a more strict make syntax-check
rule that will detect trailing blank lines.

docs/devhelp/devhelp.xsl

@@ -123,5 +123,3 @@
   </xsl:template>
 
 </xsl:stylesheet>
-
-