xdg_portal: Drop the ridiculous dependency tree - part 2

[PolyMeilex]

Now that dbus/async deps are dropped (#286), we can also drop Wayland deps, this drops our dependency tree to:

rfd
├── libc v0.2.172
├── log v0.4.27
├── pollster v0.4.0 (could also be dropped as it's posible to implement it in a couple of lines)
└── raw-window-handle v0.6.2

Final compile times with both MRs applied:

before: 19s
after: 0.7s

blocked by: #286