dsync: Removed periodic commits while importing.

The problem is that the current algorithm doesn't handle it correctly. If
there already are some mails that exist locally, or remote has duplicate
mails, the messages may not be saved in the UID order, and if there's a
commit between such wrong ordering, the UIDs get renumbered.

src/doveadm/dsync/dsync-mailbox-import.c

@@ -15,8 +15,6 @@
 #include "dsync-mailbox.h"
 #include "dsync-mailbox-import.h"
 
-#define DSYNC_COMMIT_MSGS_INTERVAL 100
-
 struct importer_mail {
 	const char *guid;
 	uint32_t uid;
@@ -1553,13 +1551,6 @@ dsync_mailbox_import_saved_uid(struct dsync_mailbox_importer *importer,
 	if (importer->highest_wanted_uid < uid)
 		importer->highest_wanted_uid = uid;
 	array_append(&importer->wanted_uids, &uid, 1);
-
-	/* commit the transaction once in a while, so if we fail we don't
-	   rollback everything. */
-	if (array_count(&importer->wanted_uids) % DSYNC_COMMIT_MSGS_INTERVAL == 0) {
-		if (dsync_mailbox_import_commit(importer, FALSE) < 0)
-			importer->failed = TRUE;
-	}
 }
 
 static bool