samples: power_mgmt: Remove redundant sample power_hooks

This sample was created intially when there were no other
samples in place to enable the CONFIG flags to build code
inside those flags. However, those CONFIG flags are now
guarded with corresponding "SUPPORTED" flags which are
enabled based in Kconfigs of socs based on their support
for that power feature. This app is for x86 and those
features will not get enabled for this configuration. If
it is still required, then we would need to fake such
support in Kconfig.board of qemu_x86. Removing it, because
those flags will get enabled by sample and test apps of
socs that support the power features, causing code inside
them to get built.

Change-Id: I647be9289a49d69880811abee499a4efd61bbc6a
Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>