[omnibox] Turn off Placeholder-text-while-empty feature flag

We had this enabled by default in 77, since we were presuming we would
launch this feature.

We're not so sure now, so turning it off by default.

Bug: 958655
Change-Id: I77be67f4cb883413ac225c569d3df7a3017d5ba8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752297Reviewed-by: Dan Beam <dbeam@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686581}

components/omnibox/common/omnibox_features.cc

@@ -246,7 +246,7 @@ const base::Feature kUIExperimentSwapTitleAndUrl{
 // are exceptions in this regard and this experiment makes this more consistent.
 const base::Feature kUIExperimentShowPlaceholderWhenCaretShowing{
     "OmniboxUIExperimentShowPlaceholderWhenCaretShowing",
-    base::FEATURE_ENABLED_BY_DEFAULT};
+    base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Feature used to enable speculatively starting a service worker associated
 // with the destination of the default match when the user's input looks like a