This aligns with how the ios recipe module is used in Chromium.
It should prevent breakages like one we had recently.
It also means we're no longer setting symbol_level=1 explicitly.
The default is 0 (no symbols), which is now what's being used.
Also move all the directories containing JSON files into
tools-webrtc/ios/bots to make it clearer (and more similar to
Chromium).
BUG=webrtc:7140, webrtc:7161
NOTRY=True
Review-Url: https://codereview.webrtc.org/2688103002
Cr-Commit-Position: refs/heads/master@{#16633}