Revert "Move /default.prop to /system/etc/prop.default"

This reverts commit fad00e43.

init fails to read default.prop under recovery:
init: Couldn't load properties from /default.prop: Too many symbolic links encountered

Bug: 62525809
Change-Id: I133e9025693e3e01278ec73c8d08860fc89d314b
(cherry picked from commit 88c9dddd)