Revert "dt-bindings: mailbox: qcom-ipcc: add missing properties into example"

This reverts commit b20eee62. The
example has just been removed altogether in the mailbox tree.

Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>