Other: Remove env.isEdge. Closes ckeditor/ckeditor5#6202.

Remove some special cases for Edge, as since it's Chromium-based now, it behaves closer to others.

tests/mediaembedediting.js

@@ -10,7 +10,6 @@ import MediaEmbedEditing from '../src/mediaembedediting';
 import { setData as setModelData, getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 import { getData as getViewData } from '@ckeditor/ckeditor5-engine/src/dev-utils/view';
 import normalizeHtml from '@ckeditor/ckeditor5-utils/tests/_utils/normalizehtml';
-import env from '@ckeditor/ckeditor5-utils/src/env';
 
 describe( 'MediaEmbedEditing', () => {
 	let editor, model, doc, view;
@@ -54,11 +53,6 @@ describe( 'MediaEmbedEditing', () => {
 		}
 	};
 
-	beforeEach( () => {
-		// Most tests assume non-edge environment but we do not set `contenteditable=false` on Edge so stub `env.isEdge`.
-		sinon.stub( env, 'isEdge' ).get( () => false );
-	} );
-
 	afterEach( () => {
 		sinon.restore();
 	} );