Remove blink_tests target.

Remove blink_tests target.

We need to have a single target called 'blink_tests' to avoid name
collision in the GN build.

Because of that it was decided to keep the Chromium's and remove this one in
Blink.

BUG=483171
TEST=build/gyp_chromium && gn gen out-gn/Debug
R=dpranke@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=195357

[tfarina, 2015-05-13 00:15:53]

Depends on https://codereview.chromium.org/1129653004/

[Dirk Pranke, 2015-05-13 00:39:57]

lgtm

[tfarina, 2015-05-14 14:38:40]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-05-14 14:38:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1136343002/1

[commit-bot: I haz the power, 2015-05-14 16:01:00]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=195357