convert log_ref_write_fd() to use strbuf

Since we don't care about how many bytes were written, simplify the return
value logic.

log_ref_write_fd() was written long before strbuf was fleshed out. Remove
the old manual buffer management code and replace it with strbuf(). Also
update copy_reflog_msg() which is called only by log_ref_write_fd() to use
strbuf as it keeps things consistent.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index dd83431..17a5260 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -91,11 +91,10 @@ enum peel_status {
 enum peel_status peel_object(const struct object_id *name, struct object_id *oid);
 
 /*
- * Copy the reflog message msg to buf, which has been allocated sufficiently
- * large, while cleaning up the whitespaces.  Especially, convert LF to space,
- * because reflog file is one line per entry.
+ * Copy the reflog message msg to sb while cleaning up the whitespaces.
+ * Especially, convert LF to space, because reflog file is one line per entry.
  */
-int copy_reflog_msg(char *buf, const char *msg);
+void copy_reflog_msg(struct strbuf *sb, const char *msg);
 
 /**
  * Information needed for a single ref update. Set new_oid to the new