ASoC: Remove name-prefix.txt

Since schema name-prefix.yaml is available and references are updated,
remove txt based doc.
Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Rob Herring <robh+dt@kernel.org>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1630686919-19495-4-git-send-email-spujar@nvidia.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/name-prefix.txt

-Name prefix:
-
-Card implementing the routing property define the connection between
-audio components as list of string pair. Component using the same
-sink/source names may use the name prefix property to prepend the
-name of their sinks/sources with the provided string.
-
-Optional name prefix property:
-- sound-name-prefix : string using as prefix for the sink/source names of
-		      the component.
-
-Example: Two instances of the same component.
-
-amp0: analog-amplifier@0 {
-	compatible = "simple-audio-amplifier";
-	enable-gpios = <&gpio GPIOH_3 0>;
-	sound-name-prefix = "FRONT";
-};
-
-amp1: analog-amplifier@1 {
-	compatible = "simple-audio-amplifier";
-	enable-gpios = <&gpio GPIOH_4 0>;
-	sound-name-prefix = "BACK";
-};