client: update obsolete comments
1) there is nothing like main thread since
3c7e8bfbb4745315b7bcbf69fa746c3d6718c305 anymore, so remove
it from documentation and update the doc accordingly.
2) use calling 'default queue' instead of 'main queue'. In the code
we use display->default_queue, so it'll be easier the understand.
3) update some obsolete or unprecise pieces of documentation
v2. Not only remove out-of-date comment, but fix/remove more
things across the wayland-client.[ch]
v3. fixes (rephrasing unclear paragraphs etc.)
according to Pakka Paalanen notes (thanks)
Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>