First of all, because it shouldn't be doing that. Second, it was
buggy and was passing the tuple returned by get_input_location to
download_file which doesn't accept tuples (instead it should be
passed the photo object so that download_file could return dc_id
and input file location itself).
It's the only way to properly clean all background tasks,
which the library makes heavy use for in MTProto/Connection
send and receive loops.
Some parts of the code even relied on the fact that it was
asynchronous (it used to return a future so you could await
it and not be breaking).
It's automatically syncified to reduce the damage of being
a breaking change.
These two occur when replying to an inline query with a photo and
InputBotInlineMessageMediaAuto empty message, and passing URLs to
PNGs that may not be accessible (i.e. 403 from pixiv).
