doc/codecs: Cosmetics in the flags2 description

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/codecs: Remove no longer existing options

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/codecs: Add ignorecrop

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/codecs: Add missing mpeg2 aac profiles

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