Remove i argument in flip boilerplate code

[obadakhalili]

flips spec function doesn't specify a second argument i, and the same is true for np.flip, which has a second argument to specify the dim to be flipped and it isn't applicable here since the requirement is only to support vectors.

So either the flip boilerplate code has to be updated, or the spec function. I can change other files if necessary.

[obadakhalili]

It is worth noting that the same problem is in diff. The boilerplate code specifies an i argument but the spec code and the numpy example don't have this i argument.