Delete all Braintree code

We never launched this, don't planning on launching it now anyway, and it's rotted over the past two years anyway.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202993577

java/google/registry/config/files/default-config.yaml

@@ -246,21 +246,6 @@ misc:
   # hosts from being used on domains.
   asyncDeleteDelaySeconds: 90
 
-# Braintree is a credit card payment processor that is used on the registrar
-# console to allow registrars to pay their invoices.
-braintree:
-  # Merchant ID of the Braintree account.
-  merchantId: example
-
-  # Public key used for accessing Braintree API (this is found on their site).
-  publicKey: example
-
-  # A map of JODA Money CurrencyUnits, specified in three letter ISO-4217
-  # format, to Braintree account IDs (each account is limited to a single
-  # currency). For example, one entry might be:
-  #   USD: accountIdUsingUSD
-  merchantAccountIdsMap: {}
-
 kms:
   # GCP project containing the KMS keyring. Should only be used for KMS in
   # order to keep a simple locked down IAM configuration.

java/google/registry/config/files/nomulus-config-production-sample.yaml

@@ -57,15 +57,5 @@ registrarConsole:
 misc:
   sheetExportId: placeholder
 
-# You only need to specify this section if using Braintree.
-braintree:
-  merchantId: placeholder
-  publicKey: placeholder
-  # Only include currencies that you use.
-  merchantAccountIdsMap:
-    EUR: placeholder
-    JPY: placeholder
-    USD: placeholder
-
 kms:
   projectId: placeholder

java/google/registry/config/files/nomulus-config-unittest.yaml

@@ -19,8 +19,3 @@ caching:
   staticPremiumListMaxCachedEntries: 50
   eppResourceCachingEnabled: true
   eppResourceCachingSeconds: 0
-
-braintree:
-  merchantAccountIdsMap:
-    USD: accountIdUsd
-    JPY: accountIdJpy