Rollup merge of rust-lang#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 dbadab5.
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 rust-lang#88332 (comment)
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.

Author: Manishearth