cpuidle/powernv : Remove dead code block

Commit 1961acad

 removes usage of
function "validate_dt_prop_sizes". This patch removes this unused
function.

Signed-off-by: Abhishek Goel <huntbag@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200706053258.121475-1-huntbag@linux.vnet.ibm.com