Revert of Remove hotword installation code at compile time if hotwording disabled.

Revert of Remove hotword installation code at compile time if hotwording disabled. (patchset #1 id:1 of https://codereview.chromium.org/1201163002/)

Reason for revert:
This CL added a compile-time check for ENABLE_HOTWORDING in a file where
ENABLE_HOTWORDING is never defined, thus the hotword shared module would
never be downloaded.

Original issue's description:
> Remove hotword installation code at compile time if hotwording disabled.
>
> If enable_hotwording is false, the code to download/install the hotword
> shared module is compiled out.
>
> (This should not change behaviour; it was already disabled at run-time,
> this just removes the installation code from the build.)
>
> BUG=491435
>
> Committed: https://crrev.com/a38832be9fef269ae1f3a191a9b69432aaf680c4
> Cr-Commit-Position: refs/heads/master@{#335843}

TBR=benwells@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=491435
Committed: https://crrev.com/1d40cc1e1c6dc12d350bf0da668f2ddcac4f5976
Cr-Commit-Position: refs/heads/master@{#335869}

[Matt Giuca, 2015-06-24 03:53:01]

Created Revert of Remove hotword installation code at compile time if hotwording
disabled.

[Matt Giuca, 2015-06-24 03:54:10]

The CQ bit was checked by mgiuca@chromium.org

[commit-bot: I haz the power, 2015-06-24 03:54:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1199343003/1

[commit-bot: I haz the power, 2015-06-24 03:55:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-24 03:55:56]

Patchset 1 (id:??) landed as
https://crrev.com/1d40cc1e1c6dc12d350bf0da668f2ddcac4f5976
Cr-Commit-Position: refs/heads/master@{#335869}