fix: remove Scalar trait bound for Matrix PartialEq and Eq

[hqurve]

I believe that the Matrix PartialEq implementation does not require that T implements Scalar.

Removing this bound would allow for users to derive PartialEq on custom generic structures without requiring that T: Scalar. For example

#[derive(PartialEq)]
struct MyCoolStructure<T>{
     m: Vector2<T>
}

[Andlon]

I can't think of anything negative consequences of this, and I like the justification.

[sebcrozet]

Thanks!