Revert of Make run-tests.py warn when it's not testing anything

Revert of Make run-tests.py warn when it's not testing anything (patchset #1 id:1 of https://codereview.chromium.org/1283513003/ )

Reason for revert:
Some bots that don't run tests (by design) don't return the test results json anymore which makes the infrastructure side fail now.

Original issue's description:
> Make run-tests.py warn when it's not testing anything
>
> I've often been confused by an "all passed" run of the test script
> when it turned out that either all the tests I cared about were skipped
> or, more likely, I mistyped the name(s) of the tests I wanted to run.
> This patch aims to fix that (and gives a useful diagnostic for the
> "all matched tests were skipped" case).
>
> R=machenbach@chromium.org
> NOTRY=true
>
> Committed: https://crrev.com/1b1de2d221a0ed23e529e91bf9fa3dc287acb2ca
> Cr-Commit-Position: refs/heads/master@{#30095}

TBR=jkummerow@chromium.org,adamk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/3444bb6485036dd09635feca34b0a14050f4c374
Cr-Commit-Position: refs/heads/master@{#30097}

[Michael Achenbach, 2015-08-10 18:54:33]

Created Revert of Make run-tests.py warn when it's not testing anything

[commit-bot: I haz the power, 2015-08-10 18:54:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1283593005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1283593005/1

[commit-bot: I haz the power, 2015-08-10 18:54:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-10 18:55:15]

Patchset 1 (id:??) landed as
https://crrev.com/3444bb6485036dd09635feca34b0a14050f4c374
Cr-Commit-Position: refs/heads/master@{#30097}