Revert "Explicitly set target_subarch for iOS."
Revert "Explicitly set target_subarch for iOS."

This reverts commit f6b7265c6bd254b1558b8e04a2c6d2c1769ef4a6.

Reason: Did not have the desired effect of resolving
https://webrtc-codereview.appspot.com/50569004/ due to incorrect
local testing. I suspect these lines need to be at another
variables-level.

TBR=tkchin@webrtc.org
BUG=4503

Review URL: https://webrtc-codereview.appspot.com/47989004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8939}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 3b71efc56e96009d8bfa80b1db2dc7da31bdca21

sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc