treewide: remove cache.h inclusion due to editor.h changes

This actually only affects sideband.c, but helps towards removing
cache.h inclusion in conjunction with some of the upcoming patches
that will be applied.

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sideband.c

@@ -1,4 +1,4 @@
-#include "cache.h"
+#include "git-compat-util.h"
 #include "color.h"
 #include "config.h"
 #include "editor.h"