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/t/t4018-diff-funcname.sh

@@ -31,8 +31,6 @@ diffpatterns="
 	cpp
 	csharp
 	css
-	dts
-	elixir
 	fortran
 	fountain
 	golang
@@ -106,6 +104,7 @@ do
 		result=success
 	fi
 	test_expect_$result "hunk header: $i" "
+		test_when_finished 'cat actual' &&	# for debugging only
 		git diff -U1 $i >actual &&
 		grep '@@ .* @@.*RIGHT' actual
 	"