docs: remove DocBook from the building system

Now that we don't have any DocBook anymore, remove it from
the building system.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Makefile b/Makefile
index 220121f..80be98c 100644
--- a/Makefile
+++ b/Makefile
@@ -1298,7 +1298,7 @@
 #
 mrproper: rm-dirs  := $(wildcard $(MRPROPER_DIRS))
 mrproper: rm-files := $(wildcard $(MRPROPER_FILES))
-mrproper-dirs      := $(addprefix _mrproper_,Documentation/DocBook scripts)
+mrproper-dirs      := $(addprefix _mrproper_,scripts)
 
 PHONY += $(mrproper-dirs) mrproper archmrproper
 $(mrproper-dirs):
@@ -1400,9 +1400,7 @@
 	@$(MAKE) $(build)=$(package-dir) help
 	@echo  ''
 	@echo  'Documentation targets:'
-	@$(MAKE) -f $(srctree)/Documentation/Makefile.sphinx dochelp
-	@echo  ''
-	@$(MAKE) -f $(srctree)/Documentation/DocBook/Makefile dochelp
+	@$(MAKE) -f $(srctree)/Documentation/Makefile dochelp
 	@echo  ''
 	@echo  'Architecture specific targets ($(SRCARCH)):'
 	@$(if $(archhelp),$(archhelp),\
@@ -1453,9 +1451,8 @@
 DOC_TARGETS := xmldocs sgmldocs psdocs latexdocs pdfdocs htmldocs mandocs installmandocs epubdocs cleandocs linkcheckdocs
 PHONY += $(DOC_TARGETS)
 $(DOC_TARGETS): scripts_basic FORCE
-	$(Q)$(MAKE) $(build)=scripts build_docproc build_check-lc_ctype
-	$(Q)$(MAKE) $(build)=Documentation -f $(srctree)/Documentation/Makefile.sphinx $@
-	$(Q)$(MAKE) $(build)=Documentation/DocBook $@
+	$(Q)$(MAKE) $(build)=scripts build_docproc
+	$(Q)$(MAKE) $(build)=Documentation $@
 
 else # KBUILD_EXTMOD