Revert "test_filejournal.cc: cleanup memory in destructor"

The finish() method for Contexts calls delete this.

This reverts commit 36028916c4630ea66007760efed8fc6c441e7af5.
test_filestore_idempotent_seqeucen: unmount prior to deleting store

Signed-off-by: Samuel Just <sam.just@inktank.com>