asyncreader: run the skip-bytes test under the race detector again

The test skipped every buffer count above 1 under -race, pointing at
golang/go#27070. That issue was closed in September 2018, so the
workaround outlived its cause: -race covered 137 of the 681 subtests.

Without the guard the race build runs all 681 and passes.

fs/asyncreader/asyncreader_test.go

@@ -13,7 +13,6 @@ import (
 	"testing/iotest"
 	"time"
 
-	"github.com/rclone/rclone/lib/israce"
 	"github.com/rclone/rclone/lib/readers"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -316,9 +315,6 @@ func TestAsyncReaderSkipBytes(t *testing.T) {
 		8000, len(data), BufferSize, 2 * BufferSize}
 
 	for buffers := 1; buffers <= 5; buffers++ {
-		if israce.Enabled && buffers > 1 {
-			t.Skip("FIXME Skipping further tests with race detector until https://github.com/golang/go/issues/27070 is fixed.")
-		}
 		t.Run(fmt.Sprintf("%d", buffers), func(t *testing.T) {
 			for _, initialRead := range initialReads {
 				t.Run(fmt.Sprintf("%d", initialRead), func(t *testing.T) {