lmkd: Remove redundant free swap and free memory check

lmkd can't kill processes because it has compare the size between free swap and free memory. Free swap is often larger than the free memory when system is under low memory with less swap-backed or swappable pages and finally leads to I/O thrashing.

Test: TreeHugger
Bug: 124727769
Change-Id: Ia2848859aa97a24bd13c704acee4b86cd2d3f647