MSC2582: Remove mimetype from EncryptedFile object (#2582)

* add proposal

* Update proposals/2582-remove-mimetype-from-encrypted-file.md

Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>

* Update proposals/2582-remove-mimetype-from-encrypted-file.md

Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>

Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>

proposals/2582-remove-mimetype-from-encrypted-file.md

@@ -0,0 +1,12 @@
+# Remove `mimetype` from `EncryptedFile` object
+
+
+## Proposal
+The example in the spec currently lists `mimetype` in the [examples for `EncryptedFile`](https://matrix.org/docs/spec/client_server/r0.6.1#extensions-to-m-message-msgtypes) but not in
+the object definition. As that is duplicate information of the `info` block of file events, the
+mimetype should just be removed alltogether.
+
+
+## Potential issues
+Some clients might depend on this.  However, as of August 2021, all known clients have
+been confirmed to not use this.