Retire ImportantFile.DeleteOnCloseError histogram.

It tells us that failures are due to I/O errors, access denied errors,
and other things we can't do anything about (likely odd drivers, too).

R=chromium-metrics-reviews@google.com, gab@chromium.org

Bug: 1156213
Change-Id: If4fb97d44d8b9a59db48239c68e69a56f59cd462
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2609143
Commit-Queue: Greg Thompson <grt@chromium.org>
Auto-Submit: Greg Thompson <grt@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841442}

base/files/important_file_writer.cc

@@ -124,12 +124,9 @@ void DeleteTmpFileWithRetry(File tmp_file,
   if (tmp_file.IsValid()) {
     if (tmp_file.DeleteOnClose(true))
       return;
-    // The file was opened with exclusive r/w access, so it would be very odd
-    // for this to fail.
-    UmaHistogramExactLinearWithSuffix(
-        "ImportantFile.DeleteOnCloseError", histogram_suffix,
-        -File::GetLastFileError(), -File::FILE_ERROR_MAX);
-    // Go ahead and close the file. The call to DeleteFile below will basically
+    // The file was opened with exclusive r/w access, so failures are primarily
+    // due to I/O errors or other phenomena out of the process's control. Go
+    // ahead and close the file. The call to DeleteFile below will basically
     // repeat the above, but maybe it will somehow succeed.
     tmp_file.Close();
   }

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -6793,7 +6793,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="ImportantFile.DeleteOnCloseError" enum="PlatformFileError"
-    expires_after="2021-01-19">
+    expires_after="M89">
+  <obsolete>
+    Removed in M89.
+  </obsolete>
   <owner>grt@chromium.org</owner>
   <owner>xaerox@yandex-team.ru</owner>
   <summary>