Revert "[Nearby] Observe screen idle state events."

This reverts commit 93a5fc5881512ffff499744b5c0f6859e35cef74.

Reason for revert: Reports that discovery and advertising are not starting because the screen is being incorrectly reported as being off. See crbug.com/1170644

Original change's description:
> [Nearby] Observe screen idle state events.
>
> This change lets us observe screen idle state (on/off state) so that
> we can invalidate send and receive surfaces in response.
>
> This also collapses PowerClientChromeos into PowerClient since we no
> longer need to guard Chrome OS-specific functionality.
>
> Fixed: 1169262
> Change-Id: I893df57d113590c0e09a81a381c3a291b74fd00a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643918
> Reviewed-by: Ryan Hansberry <[email protected]>
> Commit-Queue: Michael Hansen <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#846278}

[email protected],[email protected],[email protected]

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1170644
Change-Id: I8d0a3ceb26afab1153ff9786a1b116f5d4c448ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2650140
Reviewed-by: Ryan Hansberry <[email protected]>
Commit-Queue: Michael Hansen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#847671}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 84fc786..371014a4 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -4432,6 +4432,8 @@
       "nearby_sharing/payload_tracker.h",
       "nearby_sharing/power_client.cc",
       "nearby_sharing/power_client.h",
+      "nearby_sharing/power_client_chromeos.cc",
+      "nearby_sharing/power_client_chromeos.h",
       "nearby_sharing/share_target_discovered_callback.h",
       "nearby_sharing/share_target_info.cc",
       "nearby_sharing/share_target_info.h",