[layer/unittest] Delete old unittest

[layer/unittest] Delete old unittest

Delete negative unittest of loss layer which tests the failure of forward
without label. However, forward label is now a valid operation for loss layer.
The current reason why this unittest fails is because the number of inputs
are not managed correctly and it fails. This is managed with the previous
PR to ensure that number of inputs and outputs remain correct.
However, now it segfaults because the layer has not been initialized, and
its inputs and output havenot been assigned.

Signed-off-by: Parichay Kapoor <pk.kapoor@samsung.com>