Remove lmk.log_stats sysprop from mainline_system

It is now set on the /product partition by relevant devices.

Bug: 135569569
Test: lunch mainline_system_arm64; inspect system/etc/prop.default
Test: boot crosshatch and check the sysprop is still true via "adb shell getprop"
Change-Id: I34696977f584a65741c6002e6688d86e66a1f121
Merged-In: I34696977f584a65741c6002e6688d86e66a1f121