Convert int4 and int8 to new system

Note: purposely disabled some tests and composite support that needs to
be restored later in v5 development.

pgtype/array_test.go

@@ -5,7 +5,6 @@ import (
 	"testing"
 
 	"github.com/jackc/pgx/v5/pgtype"
-	"github.com/stretchr/testify/require"
 )
 
 func TestParseUntypedTextArray(t *testing.T) {
@@ -122,14 +121,3 @@ func TestParseUntypedTextArray(t *testing.T) {
 		}
 	}
 }
-
-// https://github.com/jackc/pgx/issues/881
-func TestArrayAssignToEmptyToNonSlice(t *testing.T) {
-	var a pgtype.Int4Array
-	err := a.Set([]int32{})
-	require.NoError(t, err)
-
-	var iface interface{}
-	err = a.AssignTo(&iface)
-	require.EqualError(t, err, "cannot assign *pgtype.Int4Array to *interface {}")
-}