vout: opengl: increase picture max for gles2
vout: opengl: increase picture max for gles2

This restriction was here because gles1 devices didn't have much memory, but
it's not the case (anymore) for gles2 devices.

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