Hello,

when I have a struct like this:

```
struct Foo<T> where T: Add<T,T> + Sub<T,T> {bar: T}
```

It's obvious that for all trait implementations this template constraint will still be true.

So why not remove this constraint from the traits, that is, replace:

```
impl<T> Add<T, T> for Foo<T> where T: Add<T,T> + Sub<T,T> {
fn add(self, rhs: T) -> T {
self.bar + rhs
}}
```

by

```
impl<T> Add<T, T> for Foo<T> {
fn add(self, rhs: T) -> T {
self.bar + rhs
}
}
```

Currently, if I do so, I get the following errors:

error: the trait

`core::ops::Add<T, T>`

is not implemented for the type`T`

error: the trait`core::ops::Sub<T, T>`

is not implemented for the type`T`

It's not so bad in this minimal example, but it becomes really painful when there is more constraints on 'T' and Foo implements more traits. Especially as we have to copy-paste all constraints even those not used in this specific trait.