ASoC: dt-bindings: stm32: dfsdm: remove stm32-adfsdm.txt binding

Device tree audio configuration for STM32 DFSDM is already
covered in the following binding:
Documentation/devicetree/bindings/iio/adc/st,stm32-dfsdm-adc.yaml
Remove stm32-adfsdm.txt obsolete binding.
Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201020155709.2621-3-olivier.moysan@st.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/st,stm32-adfsdm.txt

-STMicroelectronics Audio Digital Filter Sigma Delta modulators(DFSDM)
-
-The DFSDM allows PDM microphones capture through SPI interface. The Audio
-interface is seems as a sub block of the DFSDM device.
-For details on DFSDM bindings refer to ../iio/adc/st,stm32-dfsdm-adc.txt
-
-Required properties:
-  - compatible: "st,stm32h7-dfsdm-dai".
-
-  - #sound-dai-cells : Must be equal to 0
-
-  - io-channels : phandle to iio dfsdm instance node.
-
-Example of a sound card using audio DFSDM node.
-
-	sound_card {
-		compatible = "audio-graph-card";
-
-		dais = <&cpu_port>;
-	};
-
-	dfsdm: dfsdm@40017000 {
-		compatible = "st,stm32h7-dfsdm";
-		reg = <0x40017000 0x400>;
-		clocks = <&rcc DFSDM1_CK>;
-		clock-names = "dfsdm";
-		#interrupt-cells = <1>;
-		#address-cells = <1>;
-		#size-cells = <0>;
-
-		dfsdm_adc0: filter@0 {
-			compatible = "st,stm32-dfsdm-dmic";
-			reg = <0>;
-			interrupts = <110>;
-			dmas = <&dmamux1 101 0x400 0x00>;
-			dma-names = "rx";
-			st,adc-channels = <1>;
-			st,adc-channel-names = "dmic0";
-			st,adc-channel-types = "SPI_R";
-			st,adc-channel-clk-src = "CLKOUT";
-			st,filter-order = <5>;
-
-			dfsdm_dai0: dfsdm-dai {
-				compatible = "st,stm32h7-dfsdm-dai";
-				#sound-dai-cells = <0>;
-				io-channels = <&dfsdm_adc0 0>;
-				cpu_port: port {
-				dfsdm_endpoint: endpoint {
-					remote-endpoint = <&dmic0_endpoint>;
-				};
-			};
-		};
-	};
-
-	dmic0: dmic@0 {
-		compatible = "dmic-codec";
-		#sound-dai-cells = <0>;
-		port {
-			dmic0_endpoint: endpoint {
-				remote-endpoint = <&dfsdm_endpoint>;
-			};
-		};
-	};