[AF] Update expiring histograms

- Cardholder name fix flow prompts are still useful
- The Butter histogram's usefulness is less clear, but as it still shows
  the ratio of whether users have opted-in to Butter via the Autofill
  suggestions dropdown, IMO it can stay a little while longer.

Fixed: 1160783, 1160784
Change-Id: Ie2f1c6b3e82b0f1d11c4648fadbb4db7033f911b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2600357Reviewed-by: Chris Thompson <cthomp@chromium.org>
Commit-Queue: Jared Saul <jsaul@google.com>
Cr-Commit-Position: refs/heads/master@{#838988}

tools/metrics/histograms/histograms_xml/autofill/histograms.xml

@@ -380,7 +380,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Autofill.CardholderNameFixFlowPrompt.Events"
-    enum="AutofillCardholderNameFixFlowPromptEvent" expires_after="2021-01-31">
+    enum="AutofillCardholderNameFixFlowPromptEvent" expires_after="2021-11-30">
   <owner>jsaul@google.com</owner>
   <owner>siyua@chromium.org</owner>
   <owner>payments-autofill-team@google.com</owner>
@@ -902,7 +902,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Autofill.HadUserOptedIn_To_WalletSyncTransportServerCards"
-    enum="BooleanOptedIn" expires_after="2021-01-31">
+    enum="BooleanOptedIn" expires_after="2021-11-30">
   <owner>jsaul@google.com</owner>
   <owner>battre@chromium.org</owner>
   <summary>