[xdl]<fix>: Remove default splash screen image on Android

[bbarthec]

When a user does not provide a splash image we shouldn't show any image.
Ensured the splash screen image from Expo Client is not propagated to standalones.

Resolves https://forums.expo.io/t/how-to-remove-default-expo-splash-screen/44789/2

Test plan

I've jumped back to sdk-39 branch, build local standalone simulator app for Android.

TODOs

• test it on staging (publish xdl -rc version on npm & update in turtle on staging)
• publish xdl with this change
• (back-porting to SDK 39) rebuild sdk-39 Android shell tarball using this newer xdl version edit: this is not needed as turtle is running this piece of code
• update @expo/xdl version in turtle and ship to production

[brentvatne]

this wouldn't require deploying a new shell app tarball would it? since it's just an xdl change for code that runs against the tarball at build time, i believe.

[bbarthec]

@brentvatne, correct, as I've described in the TODOs we have to rebuild SDK-39 shel tarball and deploy it with this change 😉
edit: @brentvatne, you're observation is correct, I've misunderstood your statement and inverted it in my mind 😓

[brentvatne]

@bbarthec - i think we are not on the same page 😆 i was thinking that it would not be needed to rebuild a new shell tarball for this change. maybe let's follow up on slack to clarify, just ping me when we're both around :)