Remove destructive aspects of make distclean.

Makefile.in

@@ -376,15 +376,13 @@ clean:
 	rm -f contrib/infback9/*.gcda contrib/infback9/*.gcno contrib/infback9/*.gcov
 
 maintainer-clean: distclean
-distclean: clean zconf zconf.h.cmakein docs
+distclean: clean zconf zconf.h.cmakein
 	rm -f Makefile zlib.pc configure.log
 	-@rm -f .DS_Store
 	@if [ -f Makefile.in ]; then \
 	printf 'all:\n\t-@echo "Please use ./configure first.  Thank you."\n' > Makefile ; \
 	printf '\ndistclean:\n\tmake -f Makefile.in distclean\n' >> Makefile ; \
 	touch -r $(SRCDIR)Makefile.in Makefile ; fi
-	@if [ ! -f zconf.h.in ]; then rm -f zconf.h zconf.h.cmakein ; fi
-	@if [ ! -f zlib.3 ]; then rm -f zlib.3.pdf ; fi
 
 tags:
 	etags $(SRCDIR)*.[ch]