libstagefright: Remove assert failure for kKeyHfr

- Remove assert failure if kKeyHfr is not present in
  meta data.
- Assume normal mode recording if kKeyHfr is absent

Change-Id: I17e29c943cc8886df9e8976487c05aabc54c3129
(cherry picked from commit 9fb63299bf27bd30f8a0fab5b9c2777e4342f154)