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, 4 insertions, 4 deletions

diff --git a/tests/ui/unsized/unsized-enum2.stderr b/tests/ui/unsized/unsized-enum2.stderr
index 48cca6eb4bd..71cf782120e 100644
--- a/tests/ui/unsized/unsized-enum2.stderr
+++ b/tests/ui/unsized/unsized-enum2.stderr
@@ -320,7 +320,7 @@ error[E0277]: the size for values of type `(dyn PathHelper1 + 'static)` cannot b
 LL |     VI(Path1),
    |        ^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `Path1`, the trait `Sized` is not implemented for `(dyn PathHelper1 + 'static)`, which is required by `Path1: Sized`
+   = help: within `Path1`, the trait `Sized` is not implemented for `(dyn PathHelper1 + 'static)`
 note: required because it appears within the type `Path1`
   --> $DIR/unsized-enum2.rs:16:8
    |
@@ -343,7 +343,7 @@ error[E0277]: the size for values of type `(dyn PathHelper2 + 'static)` cannot b
 LL |     VJ{x: Path2},
    |           ^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `Path2`, the trait `Sized` is not implemented for `(dyn PathHelper2 + 'static)`, which is required by `Path2: Sized`
+   = help: within `Path2`, the trait `Sized` is not implemented for `(dyn PathHelper2 + 'static)`
 note: required because it appears within the type `Path2`
   --> $DIR/unsized-enum2.rs:17:8
    |
@@ -366,7 +366,7 @@ error[E0277]: the size for values of type `(dyn PathHelper3 + 'static)` cannot b
 LL |     VK(isize, Path3),
    |               ^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `Path3`, the trait `Sized` is not implemented for `(dyn PathHelper3 + 'static)`, which is required by `Path3: Sized`
+   = help: within `Path3`, the trait `Sized` is not implemented for `(dyn PathHelper3 + 'static)`
 note: required because it appears within the type `Path3`
   --> $DIR/unsized-enum2.rs:18:8
    |
@@ -389,7 +389,7 @@ error[E0277]: the size for values of type `(dyn PathHelper4 + 'static)` cannot b
 LL |     VL{u: isize, x: Path4},
    |                     ^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `Path4`, the trait `Sized` is not implemented for `(dyn PathHelper4 + 'static)`, which is required by `Path4: Sized`
+   = help: within `Path4`, the trait `Sized` is not implemented for `(dyn PathHelper4 + 'static)`
 note: required because it appears within the type `Path4`
   --> $DIR/unsized-enum2.rs:19:8
    |