Revert "Allow to define trait parameters via overrides"

This reverts commit faf8716.

Author: odersky

docs/docs/reference/other-new-features/trait-parameters.md

@@ -26,14 +26,12 @@ class D extends C, Greeting("Bill") // error: parameter passed twice
 Should this print "Bob" or "Bill"? In fact this program is illegal,
 because it violates the second rule of the following for trait parameters:
 
- 1. If a class `C` directly extends a parameterized trait `T`, and its superclass does not, `C` _must_ pass arguments to `T`.
+ 1. If a class `C` extends a parameterized trait `T`, and its superclass does not, `C` _must_ pass arguments to `T`.
 
- 2. If a class `C` directly or indirectly extends a parameterized trait `T`, and its superclass does as well, `C` _must not_  pass arguments to `T`.
+ 2. If a class `C` extends a parameterized trait `T`, and its superclass does as well, `C` _must not_  pass arguments to `T`.
 
  3. Traits must never pass arguments to parent traits.
 
- 4. If a class `C` extends a parameterized trait `T` only indirectly, and its superclass does not extend `T`, then all parameters of `T` must be defined via overrides.
-
 Here's a trait extending the parameterized trait `Greeting`.
 
 ```scala
@@ -53,13 +51,6 @@ The correct way to write `E` is to extend both `Greeting` and
 ```scala
 class E extends Greeting("Bob"), FormalGreeting
 ```
-Alternatively, a class could also define the `name` parameter of `Greeting` using
-an override, using rule (4) above:
-
-```scala
-class E2 extends FormalGreeting:
-   override val name: String = "Bob"
-```
 
 ## Reference