[3006] Fix error messages that are printed

doc/design/datasrc/Makefile.am

@@ -16,14 +16,14 @@ BUILT_SOURCES = \
 if HAVE_ASCIIDOC
 	$(AM_V_GEN) $(ASCIIDOC) -n $<
 else
-	@echo "*** a2x (asciidoc) is required to regenerate $(@) ***"; exit 1;
+	@echo "*** asciidoc is required to regenerate $(@) ***"; exit 1;
 endif
 
 .txt.png:
 if HAVE_PLANTUML
 	$(AM_V_GEN) $(PLANTUML) $<
 else
-	@echo "*** a2x (plantuml) is required to regenerate $(@) ***"; exit 1;
+	@echo "*** plantuml is required to regenerate $(@) ***"; exit 1;
 endif
 
 CLEANFILES = \