cmd/compile: remove go:wasmimport restriction

cmd/compile: remove go:wasmimport restriction

Removes the package restriction on go:wasmimport, allowing the
use of it globally and in user code.

Fixes #59149

Change-Id: Ib26f628dc8dafb31388005b50449e91b47dab447
Reviewed-on: https://go-review.googlesource.com/c/go/+/489255
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Eli Bendersky <eliben@google.com>
Auto-Submit: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>