Trac #33705: "make doc-clean" should remove inventory, doctrees

Followup to #29310, #33104

We could consider to extend `make doc-clean` so that it also removes
`inventory`, `doctrees`.
This should suffice to resolve incremental docbuild problems.

URL: https://trac.sagemath.org/33705
Reported by: mkoeppe
Ticket author(s): John Palmieri
Reviewer(s): Matthias Koeppe

Makefile

@@ -131,6 +131,13 @@ sage_setup-clean:
 build-clean: clean doc-clean sagelib-clean sage_docbuild-clean
 
 doc-clean:
+	if [ -f "$(SAGE_SRC)"/bin/sage-env-config ]; then \
+	    . "$(SAGE_SRC)"/bin/sage-env-config; \
+	    if [ -n "$$SAGE_LOCAL" ]; then \
+	        rm -rf "$$SAGE_LOCAL/share/doc/sage/inventory"; \
+	        rm -rf "$$SAGE_LOCAL/share/doc/sage/doctrees"; \
+	    fi; \
+	fi; \
 	cd "$(SAGE_SRC)/doc" && $(MAKE) clean
 
 # Deleting src/lib is to get rid of src/lib/pkgconfig

build/make/Makefile.in

@@ -340,9 +340,10 @@ doc-html: sagemath_doc_html
 
 # 'doc-html-no-plot': build docs without building the graphics coming
 # from the '.. plot' directive, in case you want to save a few
-# megabytes of disk space. 'doc-clean' is a prerequisite because the
-# presence of graphics is cached in src/doc/output.
-doc-html-no-plot: doc-clean
+# megabytes of disk space. Run 'make doc-clean' first because the
+# presence of graphics is cached in the built documentation.
+doc-html-no-plot:
+	(cd $(SAGE_ROOT) && $(MAKE) doc-clean)
 	+$(MAKE_REC) SAGE_DOCBUILD_OPTS="$(SAGE_DOCBUILD_OPTS) --no-plot" doc-html
 
 # Using mathjax is actually the only options, but we keep