rpi4: remove dtoverlay=disable-bt config option

Previously the instructions said to add this config option
and select a particular UART in the seL4 kernel DTS overlay.

I believe this is not necessary and so in a previous commit
to the documentation, removed the patch to the seL4 kernel
DTS.

However, the default UART selected by seL4 only works if this
line is not in the config.txt file.

Signed-off-by: Ivan Velickovic <[email protected]>

Hardware/Rpi4.md

@@ -44,7 +44,7 @@ they should be located in the root directory of this partition.
 |SSBL |bootcode.bin|Loads GPU firmware and boots GPU|<https://github.com/raspberrypi/firmware/tree/master/boot/bootcode.bin> |
 |GPU firmware |start4.elf |Loads CPU bootloader and boots CPU |<https://github.com/raspberrypi/firmware/tree/master/boot/start4.elf> |
 |Usually the Linux kernel, but could also be U-Boot |u-boot.bin |U-Boot binary| Compiled using the instructions above |
-||config.txt|U-Boot parameters |Add `arm_64bit=1`, `kernel=u-boot.bin`, and `dtoverlay=disable-bt` to the bottom of `config.txt` |
+||config.txt|U-Boot parameters |Add `arm_64bit=1` and `kernel=u-boot.bin` to the bottom of `config.txt` |
 ||uboot.env |U-Boot saved environment |Generated by U-Boot (default environment) bootcmd copied to bootcmd_orig bootcmd and bootdelay removed. This file will not exist when you first setup your SD card. |
 ||bcm2711-rpi-4-b.dtb | RPi4 device tree blob |<https://github.com/raspberrypi/firmware/tree/master/boot/bcm2711-rpi-4-b.dtb> |
 ||overlays/* | Device tree overlays |<https://github.com/raspberrypi/firmware/tree/master/boot/overlays> |