input: es_out: remove invalid assertion and fwd declaration
input: es_out: remove invalid assertion and fwd declaration

Asserts on captions on regular es

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc