MLBEDSW-7949: [MLCE] Remove duplicate cpu tensors

- If a npu op is followed by a convolution op than runs on the cpu,
the optimized file ends up containing a duplicated tensor called _cpu.
Functionality wise not a problem but the graph will look strange in a
graph viewer.

- This error was introduced when removing duplicate weights
tensors but the above use case was not considered in that patch.

- The fix is to make sure that only the weight and bias tensor are
modified.

Change-Id: I576f13650f1f9d3d50a421ab7100fc8b5ab62657
Signed-off-by: Johan Alfven <johan.alfven@arm.com>