doc: Makefile: Remove the 'prep' target

Only used to add some prereqs to the 'json' target. Put the prereqs
directly on the 'json' target instead.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

doc/Makefile

@@ -20,7 +20,7 @@ ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
 # the i18n builder cannot share the environment and doctrees with the others
 I18NSPHINXOPTS  = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
 
-.PHONY: doxy help clean content kconfig prep html dirhtml singlehtml pickle json htmlhelp qthelp devhelp epub latex latexpdf text man changes linkcheck doctest coverage gettext
+.PHONY: doxy help clean content kconfig html dirhtml singlehtml pickle json htmlhelp qthelp devhelp epub latex latexpdf text man changes linkcheck doctest coverage gettext
 
 doxy:
 	$(Q)(cat zephyr.doxyfile ; echo "STRIP_FROM_PATH=${ZEPHYR_BASE}" ) | doxygen - 2>&1 | tee doc.log
@@ -72,9 +72,6 @@ kconfig:
 	    srctree=../ ENV_VAR_BOARD_DIR=boards/*/*/ ENV_VAR_ARCH=* KERNELVERSION=1.9.99 SRCARCH=x86 \
 	    python3 scripts/genrest.py ../Kconfig reference/kconfig/
 
-
-prep: doxy content kconfig
-
 html: content kconfig
 	$(Q)$(SPHINXBUILD) -t $(DOC_TAG) -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html 2>&1 | tee -a doc.log;
 	$(Q)./scripts/filter-doc-log.sh doc.log
@@ -96,7 +93,7 @@ pickle:
 	@echo
 	@echo "Build finished; now you can process the pickle files."
 
-json: prep
+json: doxy content kconfig
 	$(SPHINXBUILD) -t $(DOC_TAG) -b json $(ALLSPHINXOPTS) $(BUILDDIR)/json
 	@rm -rf samples
 	@rm -rf boards