rootdir: init.rc: use default dirty writeout policy

This patch removed the old writeout policy tune which was never touched since
2009. In the meantime, most of Android devices are equipped with over 4GB DRAM
and very fast flash storages like UFS, which becomes more like desktop or
servers in 2009. So, it'd be worth to go back to use the default kernel configs.

Bug: 129751503
Change-Id: Idb58f5b01bbc4afd270cffba5b8912ea3565819f
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>