Keep the old TimeToFirstScrollUpdateSwapBegin2 metrics until M56 is stable

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index cff080e5dfd425942bd1887a243570a71b52307f..71ebc36ef222980f1f3657dec2a7b5a5bdb4a52c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -14414,17 +14414,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram
     name="Event.Latency.ScrollUpdate.Touch.TimeToFirstScrollUpdateSwapBegin2"
     units="microseconds">
-  <obsolete>
-    To be replaced by
-    Event.Latency.ScrollBegin.Touch.TimeToScrollUpdateSwapBegin2 in M57.
-    https://crbug.com/616482
-  </obsolete>
   <owner>tdresser@chromium.org</owner>
   <summary>
     Time between initial creation of a touch event and the start of the frame
     swap on the GPU service caused by the generated ScrollUpdate gesture event
     if that ScrollUpdate is the first such event in a given scroll gesture event
     sequence. If no swap was induced by the event, no recording is made.
+
+    To be replaced by
+    Event.Latency.ScrollBegin.Touch.TimeToScrollUpdateSwapBegin2 in M57.
+    https://crbug.com/669618
   </summary>
 </histogram>
 
@@ -14505,17 +14504,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram
     name="Event.Latency.ScrollUpdate.Wheel.TimeToFirstScrollUpdateSwapBegin2"
     units="microseconds">
-  <obsolete>
-    To be replaced by
-    Event.Latency.ScrollBegin.Wheel.TimeToScrollUpdateSwapBegin2 in M57.
-    https://crbug.com/616482
-  </obsolete>
   <owner>tdresser@chromium.org</owner>
   <summary>
     Time between initial creation of a wheel event and the start of the frame
     swap on the GPU service caused by the generated ScrollUpdate gesture event
     if that ScrollUpdate is the first such event in a given scroll gesture event
     sequence. If no swap was induced by the event, no recording is made.
+
+    To be replaced by
+    Event.Latency.ScrollBegin.Wheel.TimeToScrollUpdateSwapBegin2 in M57.
+    https://crbug.com/669618
   </summary>
 </histogram>