Editorial: GetValue and PutValue do not need to unwrap Completion Records

[bakkot]

https://github.com/tc39/ecma262/pull/2744 removed almost every case where GetValue or PutValue was passed a completion record, instead explicitly unwrapping on the previous line or lines. This removes the final three cases and then updates the definitions of those algorithms so that they do not need to handle being passed Completion Records.

[bakkot]

InitializeReferencedBinding also calls ReturnIfAbrupt on its 2 parameters, so it might make sense to include it in this PR.

Done. In the process I marked initialization of let x; and let x = 0; as infallible (in https://github.com/tc39/ecma262/pull/2842/commits/73f2743ebb27e462bc5f922bf2aa34508e474fef), which I am pretty sure is true.