Replace uses of @code in Javascript documentation with Markdown backticks

Rosie CL for []/third_party (local approval/rejection).

[]
b/71392935
Tested:
    TAP --sample for global presubmit queue
    []

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=184412611

java/google/registry/ui/externs/braintree.js

@@ -152,7 +152,7 @@ braintreepayments.ErrorField.prototype.fieldKey;
 
 
 /**
- * This will be {@code true} if the associated input is empty.
+ * This will be `true` if the associated input is empty.
  * @type {(boolean|undefined)}
  * @const
  */

java/google/registry/ui/externs/json.js

@@ -41,7 +41,7 @@ registry.json.Response = function() {};
 
 
 /**
- * Request state which can be {@code SUCCESS} or {@code ERROR}.
+ * Request state which can be `SUCCESS` or `ERROR`.
  * @type {string}
  */
 registry.json.Response.prototype.status;