MDEV-19060 : mariabackup continues, despite failing to open a tablespace

Fix mariabackup to crash if opening tablespace fails, insitead of
continuing after an error.

storage/xtradb/fil/fil0fil.cc

@@ -4827,12 +4827,6 @@ fil_load_single_table_tablespace(
 				srv_force_recovery);
 			return;
 		}
-
-		/* In mariabackup lets not crash. */
-		if (IS_XTRABACKUP()) {
-			return;
-		}
-
 		abort();
 	}