advice: move advice.graftFileDeprecated squashing to commit.[ch]

Move the squashing of the advice.graftFileDeprecated advice over to an
external variable in commit.[ch], allowing advice() to purely use the
new-style API of invoking advice() with an enum.

See 8821e90a09a (advice: don't pointlessly suggest
--convert-graft-file, 2018-11-27) for why quieting this advice was
needed. It's more straightforward to move this code to commit.[ch] and
use it builtin/replace.c, than to go through the indirection of
advice.[ch].

Because this was the last advice_config variable we can remove that
old facility from advice.c.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/commit.c b/commit.c
index 143f472..551de49 100644
--- a/commit.c
+++ b/commit.c
@@ -25,6 +25,7 @@
 static struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);
 
 int save_commit_buffer = 1;
+int no_graft_file_deprecated_advice;
 
 const char *commit_type = "commit";
 
@@ -190,7 +191,8 @@ static int read_graft_file(struct repository *r, const char *graft_file)
 	struct strbuf buf = STRBUF_INIT;
 	if (!fp)
 		return -1;
-	if (advice_graft_file_deprecated)
+	if (!no_graft_file_deprecated_advice &&
+	    advice_enabled(ADVICE_GRAFT_FILE_DEPRECATED))
 		advise(_("Support for <GIT_DIR>/info/grafts is deprecated\n"
 			 "and will be removed in a future Git version.\n"
 			 "\n"