Make the reply preview not an overlay on the timeline anymore

As users can't scroll down all the way down to the timeline like this to
see the last message (and perhaps adjust their reply to it)

This also remove the wrapper div as it is not needed anymore

res/css/views/rooms/_ReplyPreview.scss

@@ -15,10 +15,6 @@ limitations under the License.
 */
 
 .mx_ReplyPreview {
-    position: absolute;
-    bottom: 0;
-    z-index: 1000;
-    width: 100%;
     border: 1px solid $primary-hairline-color;
     background: $primary-bg-color;
     border-bottom: none;

res/css/views/rooms/_SendMessageComposer.scss

@@ -44,10 +44,5 @@ limitations under the License.
             overflow-y: auto;
         }
     }
-
-    .mx_SendMessageComposer_overlayWrapper {
-        position: relative;
-        height: 0;
-    }
 }
 

src/components/views/rooms/SendMessageComposer.js

@@ -444,9 +444,7 @@ export default class SendMessageComposer extends React.Component {
     render() {
         return (
             <div className="mx_SendMessageComposer" onClick={this.focusComposer} onKeyDown={this._onKeyDown}>
-                <div className="mx_SendMessageComposer_overlayWrapper">
                 <ReplyPreview permalinkCreator={this.props.permalinkCreator} />
-                </div>
                 <BasicMessageComposer
                     ref={this._setEditorRef}
                     model={this.model}