Bug 1778983 - Remove useless ProcessPendingRestyles call. r=boris

That was about XBL constructors being able to run script. But XBL is
gone and this should just be wasted work.

I want to land this in preparation for container queries substantially
changing the model here.

Differential Revision: https://phabricator.services.mozilla.com/D151495

layout/base/PresShell.cpp

@@ -4333,29 +4333,6 @@ void PresShell::DoFlushPendingNotifications(mozilla::ChangesToFlush aFlush) {
       LAYOUT_TELEMETRY_RECORD_BASE(Restyle);
 
       mPresContext->RestyleManager()->ProcessPendingRestyles();
-    }
-
-    // Now those constructors or events might have posted restyle
-    // events.  At the same time, we still need up-to-date style data.
-    // In particular, reflow depends on style being completely up to
-    // date.  If it's not, then style reparenting, which can
-    // happen during reflow, might suddenly pick up the new rules and
-    // we'll end up with frames whose style doesn't match the frame
-    // type.
-    if (MOZ_LIKELY(!mIsDestroying)) {
-      nsAutoScriptBlocker scriptBlocker;
-      Maybe<uint64_t> innerWindowID;
-      if (auto* window = mDocument->GetInnerWindow()) {
-        innerWindowID = Some(window->WindowID());
-      }
-      AutoProfilerStyleMarker tracingStyleFlush(std::move(mStyleCause),
-                                                innerWindowID);
-      PerfStats::AutoMetricRecording<PerfStats::Metric::Styling> autoRecording;
-      LAYOUT_TELEMETRY_RECORD_BASE(Restyle);
-
-      mPresContext->RestyleManager()->ProcessPendingRestyles();
-      // Clear mNeedStyleFlush here agagin to make this flag work properly for
-      // optimization since the flag might have set in ProcessPendingRestyles().
       mNeedStyleFlush = false;
     }