Revert "ANDROID: vendor_hook: Add hook in si_swapinfo()"

This reverts commit ed2b11d6.

The hook android_vh_si_swapinfo 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: 234214858
Cc: Bing Han <bing.han@transsion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ib474a0911dd97d54d2f086258e9d53ddd3451967