vpx_ios/README.VPXExample: Correct behavior info.

The README file was written before video timing was added. Since video now
plays at input framerate, remove the incorrect information.

Change-Id: I5de99fbf0f6d43671825aefd3ece59d553eed79a
vpx_ios/README.VPXExample: Correct 2 more mistakes.

- The perils of TBR: Missed part of a problem. Removed the last remaining
  reference to VPXExample lacking playback timing.
- Updated number of targets we build for the framework (6 to 5; removed armv6).

Change-Id: I8adf3416ee87105cdd1359732bf86454d89efe5d