revert(3p/git): Revert merge of git upstream at v2.26.2

This causes cgit to serve error pages, which is undesirable.

This reverts commit 5229c9b232, reversing
changes made to f2b211131f.

third_party/git/Documentation/Makefile

@@ -77,7 +77,6 @@ API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technica
 SP_ARTICLES += $(API_DOCS)
 
 TECH_DOCS += MyFirstContribution
-TECH_DOCS += MyFirstObjectWalk
 TECH_DOCS += SubmittingPatches
 TECH_DOCS += technical/hash-function-transition
 TECH_DOCS += technical/http-protocol
@@ -124,8 +123,7 @@ ASCIIDOC_HTML = xhtml11
 ASCIIDOC_DOCBOOK = docbook
 ASCIIDOC_CONF = -f asciidoc.conf
 ASCIIDOC_COMMON = $(ASCIIDOC) $(ASCIIDOC_EXTRA) $(ASCIIDOC_CONF) \
-		-amanversion=$(GIT_VERSION) \
-		-amanmanual='Git Manual' -amansource='Git'
+		-agit_version=$(GIT_VERSION)
 TXT_TO_HTML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_HTML)
 TXT_TO_XML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_DOCBOOK)
 MANPAGE_XSL = manpage-normal.xsl
@@ -199,13 +197,11 @@ ifdef USE_ASCIIDOCTOR
 ASCIIDOC = asciidoctor
 ASCIIDOC_CONF =
 ASCIIDOC_HTML = xhtml5
-ASCIIDOC_DOCBOOK = docbook5
+ASCIIDOC_DOCBOOK = docbook45
 ASCIIDOC_EXTRA += -acompat-mode -atabsize=8
 ASCIIDOC_EXTRA += -I. -rasciidoctor-extensions
 ASCIIDOC_EXTRA += -alitdd='&\#x2d;&\#x2d;'
 DBLATEX_COMMON =
-XMLTO_EXTRA += --skip-validation
-XMLTO_EXTRA += -x manpage.xsl
 endif
 
 SHELL_PATH ?= $(SHELL)