Remove WEBCRYPTO_HMAC_KEY_HAS_LENGTH.

Remove WEBCRYPTO_HMAC_KEY_HAS_LENGTH.

This is no longer needed since >1 month ago:
https://codereview.chromium.org/205583003

BUG=245025
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=174495

[jbroman, 2014-05-16 23:55:30]

It looks like this simply got forgotten.

[eroman, 2014-05-16 23:58:27]

lgtm

[jbroman, 2014-05-20 22:06:00]

On 2014/05/16 23:58:27, eroman wrote:
> lgtm

+jochen for public/ OWNERS (abarth is OOO)

[jochen (gone - plz use gerrit), 2014-05-21 08:47:54]

lgtm

[jbroman, 2014-05-21 13:39:24]

The CQ bit was checked by jbroman@chromium.org

[jbroman, 2014-05-21 14:28:58]

The CQ bit was unchecked by jbroman@chromium.org

[jbroman, 2014-05-21 14:28:58]

The CQ bit was checked by jbroman@chromium.org

[jbroman, 2014-05-21 14:28:59]

The CQ bit was unchecked by jbroman@chromium.org

[jbroman, 2014-05-21 14:29:17]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2014-05-21 17:51:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jbroman@chromium.org/291583006/1

[commit-bot: I haz the power, 2014-05-21 23:59:02]

Change committed as 174495