avcodec/options_table: remove extradata_size from the AVOptions table

avcodec/options_table: remove extradata_size from the AVOptions table

allowing access to the size but not the extradata itself is not useful
and could lead to potential problems if writing happens through this field

Reviewed-by: Andreas Cadhalpun <andreas.cadhalpun@googlemail.com>
Reviewed-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 1f4088b28540080ce1d42345c5614be3e1a6a197)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>