ARM: dts: qcom: nexus7: remove vcss supply which never existed

Probably got in by accident, search trough documentation and kernel code
didn't found any occurences.

Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211225212000.80459-1-david@ixit.cz