cmd/compile: suppress details error for invalid variadic argument type

CL 255241 made error message involving variadic calls clearer. To do it,
we added a check that the type of variadic argument must be a slice.
That's why the compiler crashes for invalid variadic argument type.

Instead, we can just omit the details error message, and report not
enough arguments error, which matches the behavior of go/types and types2.

Fixes #46957

Change-Id: I638d7e8f031f0ee344d5d802104fd93a60aae00a
Reviewed-on: https://go-review.googlesource.com/c/go/+/331569


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>