go/types: review of call.go

The changes from the (reviewed) dev.regabi copy of call.go can be seen
by comparing patchset 1 and 4. The actual changes are removing the
"// REVIEW INCOMPLETE" marker, deleting some leftover handling of type
instantiation in Checker.call, and adding a comment that exprOrTypeList
should be refactored.

I started to refactor exprOrTypeList, but thought it best to mark this
code as reviewed before diverging from types2.

Change-Id: Icf7fbff5a8def49c5f1781472fd7ba7b73dd9a9c
Reviewed-on: https://go-review.googlesource.com/c/go/+/295531


Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>