Revert half of "ANDROID: cpu/hotplug: create vendor hook for cpu_up/cpu_down"

This reverts parts of commit f7d52eda.

The hook android_vh_cpu_down is not used by any vendor, so remove it to
help with merge issues with future LTS releases.

If this is needed by any real user, it can easily be reverted to add it
back and then the symbol should be added to the abi list at the same
time to prevent it from being removed again later.

Bug: 203756332
Bug: 176152285
Cc: Stephen Dickey <dickey@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I66e5308f32b8b11741dd4ea659cd3f79fa9a6526