Clean up AutofillUsePaymentsCustomerData flag

I can't find any flag usage around, but I also can't find the CL that
removed the flag usage.  It seems the flag was all that's left here, so
I've removed it.

Bug: 870936
Change-Id: Id898d7aff788324cc986e85a6923882e6fcf6fe0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1639603
Commit-Queue: Jared Saul <jsaul@google.com>
Reviewed-by: Anne Lim <annelim@google.com>
Cr-Commit-Position: refs/heads/master@{#665761}

components/autofill/core/common/autofill_payments_features.cc

@@ -165,10 +165,5 @@ const base::Feature kAutofillUpstreamEditableExpirationDate{
     "AutofillUpstreamEditableExpirationDate",
     base::FEATURE_DISABLED_BY_DEFAULT};
 
-// Controls whether the PaymentsCustomerData is used to make requests to
-// Google Payments.
-const base::Feature kAutofillUsePaymentsCustomerData{
-    "AutofillUsePaymentsCustomerData", base::FEATURE_ENABLED_BY_DEFAULT};
-
 }  // namespace features
 }  // namespace autofill

components/autofill/core/common/autofill_payments_features.h

@@ -42,7 +42,6 @@ extern const base::Feature kAutofillUpstreamDisallowElo;
 extern const base::Feature kAutofillUpstreamDisallowJcb;
 extern const base::Feature kAutofillUpstreamEditableCardholderName;
 extern const base::Feature kAutofillUpstreamEditableExpirationDate;
-extern const base::Feature kAutofillUsePaymentsCustomerData;
 
 extern const char kAutofillSaveCreditCardUsesImprovedMessagingParamName[];
 extern const char