1. Fix mild ambiguity in 15.1 (see http://goo.gl/1Uxr1)
2. Strike 15.0 text no longer germane to the dixie
   reference decoder.

Change-Id: I7d20ff4325d1bd0e8718e8d7133890aac07cde0b
modified:   text_src/15.00__vp8-bitstream__loop-filter.txt
modified:   text_src/15.01__vp8-bitstream__filter-geometry-and-overall-procedure.txt