bfcache: Stop manually enabling the "WakeLock" Blink feature.

Screen Wake Locks were marked as a stable feature in r763697 ("[wakelock]
Mark ScreenWakeLock feature as stable"), so it is no longer necessary to
manually enable it support for them here.

Change-Id: I69b0578349918bd9701788cc3c792c457f506f55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633052
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844095}

content/browser/back_forward_cache_browsertest.cc

@@ -171,7 +171,6 @@ class BackForwardCacheBrowserTest : public ContentBrowserTest,
     command_line->AppendSwitchASCII(
         switches::kAutoplayPolicy,
         switches::autoplay::kNoUserGestureRequiredPolicy);
-    command_line->AppendSwitchASCII(switches::kEnableBlinkFeatures, "WakeLock");
     ContentBrowserTest::SetUpCommandLine(command_line);
   }