Remove the deprecated Alt+Shift shortcut completely

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 35b3c77107264ab91d2e3857942a0935bf1b0875..c595e27a5beb7d526435809bb3ca2a51dbf04d2b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1572,9 +1572,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     enum="DeprecatedAcceleratorUsage">
   <owner>afakhry@chromium.org</owner>
   <summary>
-    The switch to the next IME action has two accelerators:   - Shift+Alt which
-    is deprecated.   - Ctrl+Shift+Space which is new. This histogram shows the
-    number of times each accelerator (deprecated and new) is used.
+    Obsolete since M58. The switch to the next IME action has two accelerators:

[James Cook, 2017/01/27 16:40:30]

I think you need to add an <obsolete> tag, e.g.

 <obsolete>
    Deprecated 12/2016 in Issue 672205 with the addition of
    Accessibility.ModeFlag.
  </obsolete>

[afakhry, 2017/01/27 17:27:41]

Done.

+    - Shift+Alt which is deprecated.   - Ctrl+Shift+Space which is new. This
+    histogram shows the number of times each accelerator (deprecated and new) is
+    used.
   </summary>
 </histogram>