Replace the selected range instead of force-setting it

This gives people the option of cutting parts or all of their message.

src/components/views/rooms/BasicMessageComposer.js

@@ -209,9 +209,8 @@ export default class BasicMessageEditor extends React.Component {
             const selectedParts = range.parts.map(p => p.serialize());
             event.clipboardData.setData("application/x-riot-composer", JSON.stringify(selectedParts));
             if (type === "cut") {
-                // Remove the text from the composer
-                const {caret} = getCaretOffsetAndText(this._editorRef, selection);
-                this.props.model.update("", event.inputType, caret);
+                // Remove the text, updating the model as appropriate
+                replaceRangeAndMoveCaret(range, []);
             }
             event.preventDefault();
         }