util: remove outdated flightcontrol test assertion.

The test was making an assertion that is no longer expected to always be
true after moby#2195, which purposely made flightcontrol less deterministic.
This lead to occasional failures.

Signed-off-by: Erik Sipsma <erik@sipsma.dev>

util/flightcontrol/flightcontrol_test.go

@@ -193,15 +193,11 @@ func TestCancelBoth(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, ret1, "bar")
 
-	f2 := testFunc(100*time.Millisecond, "baz", &counter)
-	ret1, err = g.Do(context.TODO(), "foo", f2)
-	assert.NoError(t, err)
-	assert.Equal(t, ret1, "baz")
 	ret1, err = g.Do(context.TODO(), "abc", f)
 	assert.NoError(t, err)
 	assert.Equal(t, ret1, "bar")
 
-	assert.Equal(t, counter, int64(4))
+	assert.Equal(t, counter, int64(3))
 }
 
 func TestContention(t *testing.T) {