Remove visual borders between chat containers

Co-authored-by: jo-oikawa <14115185+jo-oikawa@users.noreply.github.com>

Author: Copilot

src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/media/chatViewPane.css

@@ -67,10 +67,6 @@
 /* Sessions control: stacked */
 .chat-viewpane.has-sessions-control.sessions-control-orientation-stacked {
 
-	.agent-sessions-container {
-		border-bottom: 1px solid var(--vscode-panel-border);
-	}
-
 	.agent-sessions-new-button-container {
 		/* hide new session button when stacked */
 		display: none;
@@ -82,18 +78,10 @@
 
 	&.chat-view-position-left {
 		flex-direction: row;
-
-		.agent-sessions-container {
-			border-right: 1px solid var(--vscode-panel-border);
-		}
 	}
 
 	&.chat-view-position-right {
 		flex-direction: row-reverse;
-
-		.agent-sessions-container {
-			border-left: 1px solid var(--vscode-panel-border);
-		}
 	}
 
 	.agent-sessions-new-button-container {