Remove duplicate check added by commit b2a5545b.

As this doesn't cause any harm so we decided to this clean up in HEAD only.

Author: Ádám Balogh
Discussion: https://postgr.es/m/VI1PR0702MB36631BD67559461AFDE1FEEE81920@VI1PR0702MB3663.eurprd07.prod.outlook.com

src/backend/access/transam/xlog.c

@@ -7377,7 +7377,7 @@ StartupXLOG(void)
 					 * Wake up any walsenders to notice that we are on a new
 					 * timeline.
 					 */
-					if (switchedTLI && AllowCascadeReplication())
+					if (AllowCascadeReplication())
 						WalSndWakeup();
 				}