powerpc/pseries/memhotplug: Remove unused inline function dlpar_memory_remove()

dlpar_memory_remove() is never used, so can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210514071041.17432-1-yuehaibing@huawei.com