Remove extraneous mimetype from EncryptedFile examples, per MSC2582 (#3412)

* Remove extraneous mimetype from EncryptedFile examples, per MSC2582

MSC: https://github.com/matrix-org/matrix-doc/pull/2582

* changelog

changelogs/client_server/newsfragments/3412.clarification

@@ -0,0 +1 @@
+Remove extraneous `mimetype` from `EncryptedFile` examples, as per [MSC2582](https://github.com/matrix-org/matrix-doc/pull/2582).

content/client-server-api/modules/end_to_end_encryption.md

@@ -282,7 +282,6 @@ Example:
     "body": "something-important.jpg",
     "file": {
       "url": "mxc://example.org/FHyPlCeYUSFFxlgbQYZmoEoe",
-      "mimetype": "image/jpeg",
       "v": "v2",
       "key": {
         "alg": "A256CTR",
@@ -312,7 +311,6 @@ Example:
           "key_ops": ["encrypt", "decrypt"],
           "kty": "oct"
         },
-        "mimetype": "image/jpeg",
         "url": "mxc://example.org/pmVJxyxGlmxHposwVSlOaEOv",
         "v": "v2"
       },