dt-bindings: serial: Remove obsolete nxp,lpc1850-uart.txt

nxp,lpc1850-uart.txt binding is already covered by 8250.yaml, so remove
it.
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230707221607.1064888-1-robh@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/serial/nxp,lpc1850-uart.txt

-* NXP LPC1850 UART
-
-Required properties:
-- compatible	: "nxp,lpc1850-uart", "ns16550a".
-- reg		: offset and length of the register set for the device.
-- interrupts	: should contain uart interrupt.
-- clocks	: phandle to the input clocks.
-- clock-names	: required elements: "uartclk", "reg".
-
-Optional properties:
-- dmas		: Two or more DMA channel specifiers following the
-		  convention outlined in bindings/dma/dma.txt
-- dma-names	: Names for the dma channels, if present. There must
-		  be at least one channel named "tx" for transmit
-		  and named "rx" for receive.
-
-Since it's also possible to also use the of_serial.c driver all
-parameters from 8250.txt also apply but are optional.
-
-Example:
-uart0: serial@40081000 {
-	compatible = "nxp,lpc1850-uart", "ns16550a";
-	reg = <0x40081000 0x1000>;
-	reg-shift = <2>;
-	interrupts = <24>;
-	clocks = <&ccu2 CLK_APB0_UART0>, <&ccu1 CLK_CPU_UART0>;
-	clock-names = "uartclk", "reg";
-};