Doc: remove text about txes always relayed from -whitelist

Updates text since -whitelistforcerelay was set to false by default in
PR bitcoin#15193.

src/init.cpp

@@ -457,7 +457,7 @@ void SetupServerArgs()
 #endif
     gArgs.AddArg("-whitebind=<addr>", "Bind to given address and whitelist peers connecting to it. Use [host]:port notation for IPv6", false, OptionsCategory::CONNECTION);
     gArgs.AddArg("-whitelist=<IP address or network>", "Whitelist peers connecting from the given IP address (e.g. 1.2.3.4) or CIDR notated network (e.g. 1.2.3.0/24). Can be specified multiple times."
-        " Whitelisted peers cannot be DoS banned and their transactions are always relayed, even if they are already in the mempool, useful e.g. for a gateway", false, OptionsCategory::CONNECTION);
+        " Whitelisted peers cannot be DoS banned", false, OptionsCategory::CONNECTION);
 
     g_wallet_init_interface.AddWalletOptions();