Commits 957a593c and
11828b88 made the flv demuxer export
a certain flag as side data to be used by the nellymoser decoder for
mid-stream sample rate changes. It used a custom side data type 'F' that
was never officially documented.

Yet since 2215c39e (merged in commit
52c522c7) this information is exported
via the properly documented AV_PKT_DATA_PARAM_CHANGE side data.
The merge commit therefore stopped exporting the 'F' sidedata; yet the
changes in the Nellymoser decoder (which are now dead code (and would
become dangerous if lots of new side data types were added)) have not
been removed. This commit does this.
Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>