This cl removes a lot of unused functionality in SystemInfo and reduces dependencies.
There's duplicate functionality in this class and WebRTC's CpuInfo class, so I'm consolidating the two implementations.
The CpuInfo interface will still exist since it's being used from Chrome to initialize the core count before the sandbox is engaged.
With this change, the SystemInfo class will get the benefit too of this initialization.
NOTRY=true
(using no try due to a dead android try bot)
Review URL: https://codereview.webrtc.org/1286163003
Cr-Commit-Position: refs/heads/master@{#9743}
