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/contrib/completion/git-prompt.sh

@@ -429,7 +429,11 @@ __git_ps1 ()
 		__git_eread "$g/rebase-merge/head-name" b
 		__git_eread "$g/rebase-merge/msgnum" step
 		__git_eread "$g/rebase-merge/end" total
-		r="|REBASE"
+		if [ -f "$g/rebase-merge/interactive" ]; then
+			r="|REBASE-i"
+		else
+			r="|REBASE-m"
+		fi
 	else
 		if [ -d "$g/rebase-apply" ]; then
 			__git_eread "$g/rebase-apply/next" step