ZTS: Fix removal_cancel.ksh

Create a larger file to extend the time required to perform the
removal. Occasional failures were observed due to the removal
completing before the cancel could be requested.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Igor Kozhukhov <igor@dilos.org>
Closes #9259