Revert of mac: Switch the default build configuration to use the 10.10 SDK. (patchset...

Revert of mac: Switch the default build configuration to use the 10.10 SDK. (patchset #2 id:20001 of https://codereview.chromium.org/1246743003/)

Reason for revert:
Causes gclient runhooks to fail on bots that don't have the 10.10 SDK (even though they don't need to compile)

Original issue's description:
> mac: Switch the default build configuration to use the 10.10 SDK.
>
> This change is intended to be temporary. The goal is to release a Canary
> compiled against the 10.10 SDK, and then to revert this CL.
>
> BUG=463170
>
> Committed: https://crrev.com/42ba22e0b8e87f758804537f64db23ff6438e451
> Cr-Commit-Position: refs/heads/master@{#340992}

TBR=thakis@chromium.org,amineer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=463170

Review URL: https://codereview.chromium.org/1254123003

Cr-Commit-Position: refs/heads/master@{#341003}