dt-bindings: xilinx: Remove uartlite from xilinx.txt

dt-bindings: xilinx: Remove uartlite from xilinx.txt

current-speed description has been added to uartlite description by commit
3de536a8c365 ("dt-bindings: serial: uartlite: Add properties for
synthesis-time parameters") that's why no reason to have in xilinx.txt too.

Fixes: 3de536a8c365 ("dt-bindings: serial: uartlite: Add properties for synthesis-time parameters")
Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/aa0b7f9a851c6b8d11f37050f84e0ec69cfa72a2.1738600116.git.michal.simek@amd.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>