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We already had implementations of some of the functions, and I didn't
bother rewriting them when we added sysinfo(2). Ross Anderson said in
https://www.lightbluetouchpaper.org/2016/07/29/yet-another-android-side-channel/
that we should "simply disable access to all procfs files", which made
me curious how many places we use /proc in bionic. This is the one that's
obviously unnecessary. The others I'm not aware of alternative APIs for.

Change-Id: Ia64f36b76f29a7a1dd67845270a5472e121aae10