Revert "lowmemorykiller.c: miss commit. +Wait for memory to be freed (faux123)"

This reverts commit 57c0e9b020b04a0c64ee46aa48f06d67815ae9dd.
Revert "Backport lowmemorykiller from Linux 3.4.29"

This reverts commit 4d85b026414710f8e433e1c4355c8698ac02460a.