[Wasm GC] Fix RemoveUnusedModuleEffects struct field reads with call.without.effects

[kripken]

If we see

(struct.new $A
  (call $call.without.effects ;; intrinsic
    (ref.func $getter)
  )
)

then we can ignore side effects in that call, as the intrinsic tells us to. However,
that function is still called (it will be called normally, after intrinsics are lowered
away), and we should not remove it.

We can perhaps do better here, but I'm not sure yet. Leaving that as a TODO.

This fixes breakage on J2Wasm.