Auto merge of #13405 - ashrko619:textencoder-encoding, r=Ms2ger

Removed support for UTF-16 in TextEncoder

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #13231  (github issue number if applicable).

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components/script/dom/webidls/TextEncoder.webidl

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /* https://encoding.spec.whatwg.org/#interface-textencoder */
-[Constructor(optional DOMString utfLabel = "utf-8"), Exposed=(Window,Worker)]
+[Constructor, Exposed=(Window,Worker)]
 interface TextEncoder {
    readonly attribute DOMString encoding;
    [NewObject]