[nrf noup] Bluetooth: Mesh: remove legacy adv support

Removes explicit support for the legacy advertiser due
to incompatibility with SDC.

The legacy advertiser can be used (experimentally) with the
Zephyr Link Layer enabled, but is not recommended.

Signed-off-by: Håvard Reierstad <[email protected]>

Author: HaavardRei

subsys/bluetooth/mesh/Kconfig

@@ -59,12 +59,16 @@ choice BT_MESH_ADV
 
 menuconfig BT_MESH_ADV_LEGACY
 	bool "Legacy advertising"
+	depends on BT_LL_SW_SPLIT
 	help
 	  Use legacy advertising commands for mesh sending. Legacy
-	  advertising is significantly slower than the extended advertising, but
-	  is supported by all controllers.
+	  advertising is significantly slower than the extended advertising.
 
-	  WARNING: The legacy advertiser can occasionally do more message
+	  WARNING: This feature is not supported in NCS. The legacy advertiser will not work
+	  with SDC, as attempting to start an advertisement during the scanner duty cycle
+	  will result in an error. The Zephyr Link Layer can be used experimentally as an
+	  alternative.
+	  The legacy advertiser can occasionally do more message
 	  retransmissions than requested because of limitations of HCI
 	  interface API.