nimble/transport: Remove HCI event buffer size override for extadv

We can now fragment scanned advertising PDUs into smaller reports to
fit in configured event size - no need to override this for ext adv
anymore.

X-Original-Commit: 13bc5613ed89a19da7f020005ff6df26f1d7b7f4

nimble/transport/ram/syscfg.yml

@@ -40,6 +40,3 @@ syscfg.defs:
             This is the maximum size of the data portion of HCI ACL data
             packets. It does not include the HCI data header (of 4 bytes).
         value: 255
-
-syscfg.vals.BLE_EXT_ADV:
-    BLE_HCI_EVT_BUF_SIZE: 274

nimble/transport/socket/syscfg.yml

@@ -71,6 +71,3 @@ syscfg.defs:
     BLE_SOCK_STACK_SIZE:
         description: 'Size of the HCI socket stack (units=words).'
         value: 80
-
-syscfg.vals.BLE_EXT_ADV:
-    BLE_HCI_EVT_BUF_SIZE: 274

nimble/transport/uart/syscfg.yml

@@ -66,6 +66,3 @@ syscfg.defs:
     BLE_HCI_UART_FLOW_CTRL:
         description: 'Flow control used for HCI uart interface'
         value:       HAL_UART_FLOW_CTL_RTS_CTS
-
-syscfg.vals.BLE_EXT_ADV:
-    BLE_HCI_EVT_BUF_SIZE: 274