Removes atrt-testBackup script and modifies all the testsuites which had
atrt-testBackup to just testBackup.

After the Bug#29391329 was fixed, the required path for ndb_restore binary will
be evaluated based on environment variables set and doesn't require
atrt-testBackup script to set the PATH from autotest. So,
atrt-testBackup is replaced with just testBackup in all the testsuites.

Approved by: Tiago Alves <tiago.alves@oracle.com>