Shorten audio_modem test_support target to just "test_support".

Shorten audio_modem test_support target to just "test_support".

In GN we can just do //components/audio_modem:test_support, we don't
need the 'audio_modem' redundance twice here.

Also turned it from a static library into a source set.

BUG=None
R=brettw@chromium.org

Committed: https://crrev.com/4df99d351d6f65520f49670dd89f3a13c647b24f
Cr-Commit-Position: refs/heads/master@{#339911}

[tfarina, 2015-07-20 23:37:54]

Hi Brett, could you review this to me?

[tfarina, 2015-07-22 14:21:18]

Brett, ping?

[brettw, 2015-07-22 16:04:38]

lgtm

[tfarina, 2015-07-22 17:25:56]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-07-22 17:26:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1243923002/1

[commit-bot: I haz the power, 2015-07-22 17:58:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-22 17:59:51]

Patchset 1 (id:??) landed as
https://crrev.com/4df99d351d6f65520f49670dd89f3a13c647b24f
Cr-Commit-Position: refs/heads/master@{#339911}