Remove an obsolete style declaration of .mx_ReplyChain_show (#8743)

It was added with https://github.com/matrix-org/matrix-react-sdk/pull/6291/files#diff-11808ff6468e6efa5982f414119fcc8a3a3eea4090b1a4ebda8ed6eae732418aR163

It has not been effective for unknown period, and since the layout of the area has changed, it should be able to be safely removed.

Signed-off-by: Suguru Hirahara <luixxiul@users.noreply.github.com>

res/css/views/rooms/_EventBubbleTile.scss

@@ -447,10 +447,6 @@ limitations under the License.
             flex-direction: column;
         }
 
-        .mx_ReplyChain_show {
-            order: 99999;
-        }
-
         .mx_ReplyChain {
             .mx_EventTile_reply {
                 max-width: 90%;