Remove some old stuff from doc/Makefile.am

Incidentally, this makes 'make dist' work even if --disable-documentation
is set.

[[Imported from SVN: r12945]]

doc/Makefile.am

 
 SUBDIRS = doxygen
-
 CURDIR = doc
-
 BASEDIR = ..
 
 docdir=$(datadir)/doc/dune/solvers
 
-include $(top_srcdir)/am/webstuff
-
-CLEANFILES = $(PAGES)
-
-if ! BUILD_DOCS
-# add tag to notify that dist has been build without documentation
-dist-hook:
-        echo "# No documentation included in distribution! " > $(distdir)/$(DOCUMENTATION_TAG_FILE)
-endif
+EXTRA_DIST = CMakeLists.txt
 
+include $(top_srcdir)/am/webstuff
 include $(top_srcdir)/am/global-rules