boot: zephyr: cleanup nrf52840_pca10059 configuration

Cleanup board configuration.

Signed-off-by: Emanuele Di Santo <emdi@nordicsemi.no>
diff --git a/boot/zephyr/boards/nrf52840_pca10059.conf b/boot/zephyr/boards/nrf52840_pca10059.conf
index f40c6c2..bf63bf7 100644
--- a/boot/zephyr/boards/nrf52840_pca10059.conf
+++ b/boot/zephyr/boards/nrf52840_pca10059.conf
@@ -1,5 +1,4 @@
-
-# Needed by CDC ACM
+# Serial
 CONFIG_SERIAL=y
 CONFIG_UART_NRFX=y
 CONFIG_UART_INTERRUPT_DRIVEN=y
@@ -29,6 +28,3 @@
 
 # Logging
 CONFIG_SYS_LOG_DEFAULT_LEVEL=1
-CONFIG_SYS_LOG_USB_CDC_ACM_LEVEL=1
-CONFIG_SYS_LOG_USB_DRIVER_LEVEL=1
-CONFIG_SYS_LOG_USB_DEVICE_LEVEL=1