ASoC: dt-bindings: tas2780: remove tas2780 and will merge it to tas27xx

Remove tas2780 binding documentation, the binding will be documented in
the tax27xx binding.

Signed-off-by: Raphael-Xu <13691752556@139.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220722105345.175-1-13691752556@139.com


Signed-off-by: Mark Brown <broonie@kernel.org>