Revert "Merge branch 'en/header-split-cache-h-part-3' into next"

This reverts commit 76ebce0b7a,
reversing changes made to 62e19d66fb,
in preparation for redoing the topic to make it buildable from the
source.

git.c

@@ -5,7 +5,6 @@
 #include "gettext.h"
 #include "help.h"
 #include "pager.h"
-#include "read-cache-ll.h"
 #include "run-command.h"
 #include "alias.h"
 #include "replace-object.h"