muge.4: remove BUGS section (about link/act LEDs)

Lack of functioning link and activity LEDs on devices without an EEPROM
is expected (not a bug). Quoting the EVB-LAN7850 User's Guide:

When configured with the default internal register settings, the
Ethernet Link status LEDs are not enabled.  To enable Ethernet Link
status LEDs, enable the EEPROM.

This is an artifact of the different ways in which the evaluation board
can be used. End-user USB-Ethernet adapters using the Microchip LAN78XX
or LAN7515 controllers should use an EEPROM or have OTP configuration,
if their product configuration does not match the boot default register
configuration.

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