m7spr: update ril system props

From 5.03.651.3 build.prop:
- Increase snapshot_timer to 22
- Remove ril props that do not exist in stock and don't seem to belong
  * While persist.radio.mode_pref_nv10 does exist when running strings
    on m7spr radio libs, it isn't specified in build.prop.
- Add QCOM prop "ro.ril.scan.selection.rat"
  * This does exist when running strings on m7spr radio libs

Change-Id: I7562310cea0040140b9e61c68a759fc6a042ec80