main/postmarketos-ui-sway: remove dependency on xorg-server

postmarketos-ui-sway already depends on xorg-server-xwayland for X clients. There is no need to pull in the entire X server including all necessary drivers.

This saves ~84 MiB of disk space when installing postmarketos-ui-sway on asus-me176c. X applications are still working fine through Xwayland.

Also remove explicit dependency on dbus - it is already pulled in by dependencies like lightdm or elogind and nothing in postmarketos-ui-sway depends on it specifically.

Cc: @danct12