boards: esp32s3_devkitm: remove conflicting usb_serial reference

The usb_serial node is referenced twice in the procpu dts file. The first
time the status is set to "okay", while the second it is set to "disabled".
Only the second status is honored, so the first is removed to eliminate
confusion.

Signed-off-by: Daniel Mangum <georgedanielmangum@gmail.com>