MB: Fix incorrect iOS builder names.
MB: Fix incorrect iOS builder names.

In https://codereview.webrtc.org/2239643002/ MB was turned on
for the iOS GYP bots. This exposed an incorrect config for the
iOS simulator bots in client.webrtc.

BUG=589510
NOTRY=True

Review-Url: https://codereview.webrtc.org/2245393003
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#13778}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e252d3ce3a3a14a554296f9caabc46fa9b4a2c1f

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