Disable fullscreen alert for M88

This CL disable the prevent fake login screen feature

Following concerns from leadership, we are going to disable
the fake login screen feature for M88. We will revisit in M90.

Bug: 1158574
Change-Id: I12abd81a2871da1864ad166bb2929d6f38dd9dd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2590751Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaodan Zhu <zxdan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836874}

ash/public/cpp/ash_features.cc

@@ -129,7 +129,7 @@ const base::Feature kReverseScrollGestures{"EnableReverseScrollGestures",
                                            base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kFullscreenAlertBubble{"EnableFullscreenBubble",
-                                           base::FEATURE_ENABLED_BY_DEFAULT};
+                                           base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kSystemTrayMicGainSetting{"SystemTrayMicGainSetting",
                                               base::FEATURE_ENABLED_BY_DEFAULT};