Editorial: remove API URL character encoding

As per whatwg/html#9755.

Author: annevk

docs/index.bs

@@ -2945,8 +2945,6 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
               :: Return |realmExecutionContext|.
               : The [=environment settings object/module map=]
               :: Return |workerGlobalScope|'s [=WorkerGlobalScope/module map=].
-              : The <a>API URL character encoding</a>
-              :: Return [=UTF-8=].
               : The <a>API base URL</a>
               :: Return |serviceWorker|'s [=service worker/script url=].
               : The [=environment settings object/origin=]