MDEV-7615: remove galera_sst_mode.result file

mysql-test/r/galera_sst_mode.result

-#
-# Test for mysqldump's galera-sst-mode option
-#
-#
-# MDEV-6490: mysqldump unknown option --galera-sst-mode
-#
-CREATE DATABASE bug6490;
-USE bug6490;
-CREATE TABLE t1(c1 INT);
-INSERT INTO t1 values (1);
-INSERT INTO t1 values (2);
-# Save the current gtid_binlog_state.
-# Take a dump of bug6490 database
-DROP TABLE t1;
-# Load the dump
-RESET MASTER;
-SELECT * from t1;
-c1
-1
-2
-# Compare the two gtid_binlog_state's
-# Cleanup
-DROP DATABASE bug6490;
-# End of test