Bug 1890912 - Fix warning spam in `HTMLEditor::SplitAncestorStyledInlineElementsAtRangeEdges()` r=m_kato

The cause is an expected case.  Therefore, using `NS_WARN_IF` is wrong.

Differential Revision: https://phabricator.services.mozilla.com/D207240

editor/libeditor/HTMLStyleEditor.cpp

@@ -2076,7 +2076,7 @@ HTMLEditor::SplitAncestorStyledInlineElementsAtRangeEdges(
       return result;
     }
     tracker.FlushAndStopTracking();
-    if (NS_WARN_IF(result.inspect().Handled())) {
+    if (result.inspect().Handled()) {
       auto endOfRange = result.inspect().AtSplitPoint<EditorDOMPoint>();
       if (!endOfRange.IsSet()) {
         result.inspect().IgnoreCaretPointSuggestion();