[dev.unified] cmd/compile/internal/typecheck: replace unreachable code with assert
Since the removal of -G=0 mode, IR is always well-typed. And in
well-typed IR, convlit will always returns expressions having real
types (i.e., not untyped).
Change-Id: I1ac99a88c94777829852519347a716d19af7948c
Reviewed-on: https://go-review.googlesource.com/c/go/+/413363
Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>