Revert of Check that usage isn't empty when generateKey() is called

Revert of Check that usage isn't empty when generateKey() is called (patchset #4 id:60001 of https://codereview.chromium.org/745443002/)

Reason for revert:
This patch caused the crypto/rsa-oaep-generate-non-extractable-key.html layouttest to fail on non-linux bots:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=crypto%2Frsa-oaep-generate-non-extractable-key.html&testType=layout-tests

Original issue's description:
> Check that usage isn't empty when generateKey() is called
>
> BUG=425645
>
> Committed: https://crrev.com/f723e1609b239219b3fb88e8db06562ad56a8af9
> Cr-Commit-Position: refs/heads/master@{#305350}

TBR=rsleevi@chromium.org,eroman@chromium.org,nharper@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=425645
Committed: https://crrev.com/4ec50f25659b4754cb5328d02c650944988bc598
Cr-Commit-Position: refs/heads/master@{#305374}

[pdr., 2014-11-22 21:33:47]

Created Revert of Check that usage isn't empty when generateKey() is called

[commit-bot: I haz the power, 2014-11-22 21:34:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/751883002/1

[commit-bot: I haz the power, 2014-11-22 21:34:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-22 21:35:18]

Patchset 1 (id:??) landed as
https://crrev.com/4ec50f25659b4754cb5328d02c650944988bc598
Cr-Commit-Position: refs/heads/master@{#305374}