dt-bindings: Remove unused Sigma Designs Tango bindings

The Sigma Designs Tango support has been removed, but 2 binding docs
for NAND and PCIe were missed. Remove them.

Cc: Marc Gonzalez <marc.w.gonzalez@free.fr>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-mtd@lists.infradead.org
Cc: linux-pci@vger.kernel.org
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210430153225.3366000-1-robh@kernel.org/


Signed-off-by: Rob Herring <robh@kernel.org>