* doc/Makefile.am (doc, doc-user, doc-devel)
	(doc-pdf, doc-html, doc-devel-pdf, doc-devel-html)
	(ref-doc, ref-doc-pdf, ref-doc-devel, ref-doc-devel-pdf)
	(tutorial-pdf, white-paper-pdf, ref-guide-pdf)
	(tutorial-html, white-paper-html, ref-guide-html):
	Remove (phony) targets.
	* Makefile.am (doc, tutorial): Likewise.