Remove detail from label/note that is already available in other note

Remove the "which is required by `{root_obligation}`" post-script in
"the trait `X` is not implemented for `Y`" explanation in E0277. This
information is already conveyed in the notes explaining requirements,
making it redundant while making the text (particularly in labels)
harder to read.

```
error[E0277]: the trait bound `NotCopy: Copy` is not satisfied
  --> $DIR/wf-static-type.rs:10:13
   |
LL | static FOO: IsCopy<Option<NotCopy>> = IsCopy { t: None };
   |             ^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `NotCopy`
   |
   = note: required for `Option<NotCopy>` to implement `Copy`
note: required by a bound in `IsCopy`
  --> $DIR/wf-static-type.rs:7:17
   |
LL | struct IsCopy<T:Copy> { t: T }
   |                 ^^^^ required by this bound in `IsCopy`
```
vs the prior

```
error[E0277]: the trait bound `NotCopy: Copy` is not satisfied
  --> $DIR/wf-static-type.rs:10:13
   |
LL | static FOO: IsCopy<Option<NotCopy>> = IsCopy { t: None };
   |             ^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `NotCopy`, which is required by `Option<NotCopy>: Copy`
   |
   = note: required for `Option<NotCopy>` to implement `Copy`
note: required by a bound in `IsCopy`
  --> $DIR/wf-static-type.rs:7:17
   |
LL | struct IsCopy<T:Copy> { t: T }
   |                 ^^^^ required by this bound in `IsCopy`
```

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/ui/function-pointer/unsized-ret.stderr b/tests/ui/function-pointer/unsized-ret.stderr
index 81d603f4b20..66116273ff4 100644
--- a/tests/ui/function-pointer/unsized-ret.stderr
+++ b/tests/ui/function-pointer/unsized-ret.stderr
@@ -4,7 +4,7 @@ error[E0277]: the size for values of type `str` cannot be known at compilation t
 LL |     foo::<fn() -> str, _>(None, ());
    |           ^^^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `fn() -> str`, the trait `Sized` is not implemented for `str`, which is required by `fn() -> str: Fn<_>`
+   = help: within `fn() -> str`, the trait `Sized` is not implemented for `str`
    = note: required because it appears within the type `fn() -> str`
 note: required by a bound in `foo`
   --> $DIR/unsized-ret.rs:5:11
@@ -18,7 +18,7 @@ error[E0277]: the size for values of type `(dyn std::fmt::Display + 'a)` cannot
 LL |     foo::<for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),));
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`, the trait `for<'a> Sized` is not implemented for `(dyn std::fmt::Display + 'a)`, which is required by `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a): Fn<_>`
+   = help: within `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`, the trait `for<'a> Sized` is not implemented for `(dyn std::fmt::Display + 'a)`
    = note: required because it appears within the type `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`
 note: required by a bound in `foo`
   --> $DIR/unsized-ret.rs:5:11