player: minor changes

This shouldn't change anything functionally.

Change the A/V desync message. --framedrop is enabled by default now, so
the text must be changed a little. I've never heard of audio outputs
messing up A/V sync recently, so remove that part.

Remove the unused ao_pts field.

Reorder 2 A/V sync related expressions so that they look the same.
input: stdin is 0, not 1

Oops. I can never remember this right.
manpage: mention that mp.commandv doesn't expand properties

The little lua snippet at #488 as well as the actual implementation
seems to indicate that not expanding properties is indeed the correct
behavior.  Document that.

Signed-off-by: wm4 <wm4@nowhere>