Revert "dt-bindings: irqchip: Add PRUSS interrupt controller bindings"

This reverts commit 2e00d1d2.

Drop the plain text-format binding document for the PRUSS interrupt
controller. This has been replaced by an equivalent upstream preferred
YAML-format binding document in commit 52d5b9d4 ("dt-bindings:
irqchip: Add PRU-ICSS interrupt controller bindings").

Signed-off-by: Suman Anna <s-anna@ti.com>