remove CONFIG_ANDROID_LOW_MEMORY_KILLER requirement

Kernel configuration options should include either
CONFIG_ANDROID_LOW_MEMORY_KILLER for in-kernel lowmemorykiller driver
to be used or a combination of CONFIG_MEMCG and CONFIG_MEMCG_SWAP
if userspace lmkd is preferred. It is not currently possible to express
this logical requirement in the config fragment so the
CONFIG_ANDROID_LOW_MEMORY_KILLER requirement is simply
removed for now.

Bug: 71502948

Change-Id: If022e978265465e7de75e23ac90361149398df3b
Signed-off-by: Suren Baghdasaryan <surenb@google.com>