Remove an obsolete style block related to highlighting from _IRCLayout.pcss (#10451)

* Remove an obsolete style block related to highlighting from _IRCLayout.pcss

Initially it has been added with this commit 67249e1 for the implementation of IRC layout, but the border declarations for highlighting were removed with this commit 3a2aa9d to replace the 'border-left' declaration with the 'box-shadow' declaration.

Signed-off-by: Suguru Hirahara <[email protected]>

Author: luixxiul

res/css/views/rooms/_IRCLayout.pcss

@@ -182,13 +182,6 @@ $irc-line-height: $font-18px;
         }
     }
 
-    /* Suppress highlight thing from the normal Layout. */
-    .mx_EventTile:hover.mx_EventTile_verified .mx_EventTile_line,
-    .mx_EventTile:hover.mx_EventTile_unverified .mx_EventTile_line,
-    .mx_EventTile:hover.mx_EventTile_unknown .mx_EventTile_line {
-        border-left: 0;
-    }
-
     .mx_ReplyChain {
         .mx_DisambiguatedProfile {
             width: unset;