[vlc-devel] css: update deprecated statement, fix warning

[Francois Cartegnie]

> -%define api.pure
> +%pure-parser
>  
>  %parse-param { yyscan_t scanner }
>  %parse-param { vlc_css_parser_t *css_parser }

Breaks build with some configurations (autoconf < 2.70 ?) no longer
detecting the need for API/triggering the build to make the header.

-- 
Francois Cartegnie
VideoLAN - VLC Developer