Rollup merge of #88346 - spastorino:revert-type-of-a-let2, r=jackh726

Revert "Add type of a let tait test impl trait straight in let"

This reverts commit dbadab54.
This is not part of TAITs, so, if tested should probably be done
elsewhere.

r? ````@oli-obk````

This is similar to what I was commenting here https://github.com/rust-lang/rust/pull/88332#discussion_r695939901
These is not part of TAITs so should not live in type-alias-impl-trait test directory.
I'm going to avoid adding this kind of tests in `type-alias-impl-trait` test directory and avoid thinking about them in this pass.

src/test/ui/type-alias-impl-trait/type_of_a_let2.rs

-#![feature(type_alias_impl_trait)]
-#![allow(dead_code)]
-
-// FIXME This should be under a feature flag
-
-use std::fmt::Debug;
-
-fn foo1() -> u32 {
-    let x: impl Debug = 22_u32;
-    //~^ ERROR: `impl Trait` not allowed outside of function and method return types [E0562]
-    x // ERROR: we only know x: Debug, we don't know x = u32
-}
-
-fn foo2() -> u32 {
-    let x: impl Debug = 22_u32;
-    //~^ ERROR: `impl Trait` not allowed outside of function and method return types [E0562]
-    let y: impl Debug = x;
-    //~^ ERROR: `impl Trait` not allowed outside of function and method return types [E0562]
-    same_type((x, y)); // ERROR
-    x
-}
-
-fn same_type<T>(x: (T, T)) {}
-
-fn main() {}

src/test/ui/type-alias-impl-trait/type_of_a_let2.stderr

-error[E0562]: `impl Trait` not allowed outside of function and method return types
-  --> $DIR/type_of_a_let2.rs:9:12
-   |
-LL |     let x: impl Debug = 22_u32;
-   |            ^^^^^^^^^^
-
-error[E0562]: `impl Trait` not allowed outside of function and method return types
-  --> $DIR/type_of_a_let2.rs:15:12
-   |
-LL |     let x: impl Debug = 22_u32;
-   |            ^^^^^^^^^^
-
-error[E0562]: `impl Trait` not allowed outside of function and method return types
-  --> $DIR/type_of_a_let2.rs:17:12
-   |
-LL |     let y: impl Debug = x;
-   |            ^^^^^^^^^^
-
-error: aborting due to 3 previous errors
-
-For more information about this error, try `rustc --explain E0562`.