advice: remove read uses of most global `advice_` variables

In c4a09cc9ccb (Merge branch 'hw/advise-ng', 2020-03-25), a new API for
accessing advice variables was introduced and deprecated `advice_config`
in favor of a new array, `advice_setting`.

This patch ports all but two uses which read the status of the global
`advice_` variables over to the new `advice_enabled` API. We'll deal
with advice_add_embedded_repo and advice_graft_file_deprecated
separately.

Signed-off-by: Ben Boeckel <mathstuf@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/clone.c b/builtin/clone.c
index 66fe666..c1603aa 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -786,7 +786,7 @@ static int checkout(int submodule_progress)
 		return 0;
 	}
 	if (!strcmp(head, "HEAD")) {
-		if (advice_detached_head)
+		if (advice_enabled(ADVICE_DETACHED_HEAD))
 			detach_advice(oid_to_hex(&oid));
 		FREE_AND_NULL(head);
 	} else {