MDEV-12627: innodb.innodb_bug14147491 does not do proper cleanup

Removed creation of unused backup file and unused variables.

mysql-test/suite/innodb/r/innodb_bug14147491.result

@@ -3,7 +3,6 @@ set global innodb_file_per_table=ON;
 CREATE TABLE t1 (a INT AUTO_INCREMENT PRIMARY KEY, b TEXT) ENGINE=InnoDB;
 INSERT INTO t1 (b) VALUES ('corrupt me');
 INSERT INTO t1 (b) VALUES ('corrupt me');
-# Backup the t1.ibd before corrupting
 # Corrupt the table
 Munged a string.
 Munged a string.

mysql-test/suite/innodb/t/innodb_bug14147491.test

@@ -34,9 +34,6 @@ let t1_IBD = $MYSQLD_DATADIR/test/t1.ibd;
 
 --source include/shutdown_mysqld.inc
 
---echo # Backup the t1.ibd before corrupting
---copy_file $t1_IBD $MYSQLD_DATADIR/test/t1.ibd.backup
-
 --echo # Corrupt the table
 
 perl;