db: Do not exit transaction on failure

Automatically exiting the DB transaction upon any failure is strange
since it'll kill any later attempt to commit. The commit itself should
be used to verify that everything was ok.

wallet/db.c

@@ -99,7 +99,6 @@ bool PRINTF_FMT(3, 4)
 
 	err = sqlite3_exec(db->sql, cmd, NULL, NULL, &errmsg);
 	if (err != SQLITE_OK) {
-		db->in_transaction = false;
 		tal_free(db->err);
 		db->err = tal_fmt(db, "%s:%s:%s:%s", caller,
 				  sqlite3_errstr(err), cmd, errmsg);