Disable default-features for the ndk crate

We decided to add `rwh_06` to the `default` list of features in the
`ndk` to [nudge users to upgrade], but this forces `winit` to always
(transitively) include `raw-window-handle 0.6` even if the user has
set a different `rwh_xx` feature on the `winit` crate.  `winit` already
forwards the respective `rwh_xx` feaure to the `ndk` crate anyway, so
this default should just be turned off.

At the time of writing this is the only `default` feature of the `ndk`.

[nudge users to upgrade]: rust-mobile/ndk#434 (comment)

Cargo.toml

@@ -74,7 +74,7 @@ softbuffer = "0.3.0"
 
 [target.'cfg(target_os = "android")'.dependencies]
 android-activity = "0.5.0"
-ndk = "0.8.0"
+ndk = { version = "0.8.0", default-features = false }
 ndk-sys = "0.5.0"
 
 [target.'cfg(any(target_os = "ios", target_os = "macos"))'.dependencies]