Revert "Enable checks for outdated plugins even when third-party plugin installation is not enabled"

Revert of Enable checks for outdated plugins even when third-party plugin installation is not enabled. (patchset #1 id:1 of https://codereview.chromium.org/1234223003/)

Reason for revert:
Crashes when encountering an outdated plugin on Linux/CrOS (https://crbug.com/510684 and https://crbug.com/510567).

Original issue's description:
> Enable checks for outdated plugins even when third-party plugin installation is not enabled.
>
> Even built-in plugins can be outdated, in particular if plugin metadata is updated separately from a Chrome update.
>
> BUG=509832
>
> Committed: https://crrev.com/364aa7f794daadbe497a0ad02621aa1d5a400a49
> Cr-Commit-Position: refs/heads/master@{#338869}

TBR=wfh@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=509832
Committed: https://crrev.com/fa9dc9ac45aeb564acf426b626e6398822f76a4b
Cr-Commit-Position: refs/heads/master@{#339005}

[Bernhard Bauer, 2015-07-16 09:10:04]

Created Revert of Enable checks for outdated plugins even when third-party
plugin installation is not enabled.

[commit-bot: I haz the power, 2015-07-16 09:10:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-16 09:11:50]

Patchset 1 (id:??) landed as
https://crrev.com/fa9dc9ac45aeb564acf426b626e6398822f76a4b
Cr-Commit-Position: refs/heads/master@{#339005}