Remove deprecated PPB_Messaging_1_1

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 723803e4a19c1da768887d93bd7bbd4786dd75a7..df5da581fcbac143e7ec0ec008a993d0be518611 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -56568,7 +56568,6 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1994108724" label="PPB_Flash_File_FileRef;2"/>
   <int value="1997668256" label="PPB_GLESChromiumTextureMapping(Dev);0.1"/>
   <int value="1998274350" label="PPB_Font(Dev);0.6"/>
-  <int value="2001322203" label="PPB_Messaging;1.1"/>

[bbudge, 2015/03/25 17:26:39]

Can we remove histogram values?

[dmichael (off chromium), 2015/03/25 17:38:50]

Good question; usually we should lean towards no. But it's good to remove them
when they no longer appear, yes. I verified we don't have any occurrences of
this in UMA.

[Ilya Sherman, 2015/03/25 20:42:26]

IMO, there's no need to remove this, and it can help to keep it around, just in
case you want to look at really old data that might have the label.  But, if
you're 100% sure that there's no data that has this label, and you really want
to remove it, that's fine.

   <int value="2003778556" label="PPB_MouseInputEvent;1.1"/>
   <int value="2005291722" label="PPB_NetAddress_Private;1.1"/>
   <int value="2012645499" label="PPB_Find(Dev);0.3"/>