Remove the OS() guard from ThreadIdentifierDataPthreads.cpp

In general the project should avoid using OS() guards when possible.

In this particular case both OS() and PTHREAD_KEYS_MAX are used as a guard, even though using PTHREAD_KEYS_MAX as a guard is sufficient. Not only that this solution works not just for ANDROID but also for other systems where chromium might be ported to (in or out of the tree). 

As an example the proposed change would work on HURD systems as well (the support for HURD is not maintained in the tree, but it demonstrates that the change handles those systems as well).

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177115

[lgombos, 2014-06-27 15:38:59]

PTAL - simple cleanup with a stated goal.

[abarth-chromium, 2014-06-27 16:50:14]

lgtm

[commit-bot: I haz the power, 2014-06-27 16:50:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/l.gombos@samsung.com/351683007/1

[commit-bot: I haz the power, 2014-06-27 16:53:16]

Change committed as 177115