Bevy's published crates.io crate now deploys assets

## Bevy version

0.7

## What you did

@NiklasEi discovered that the `bevy` crate is now ~10 megabytes on crates.io (up from 150 kilobytes).

## What went wrong

 This is because we added a symlink in #3705, circumventing the "assets/**/*" exclusion in the `bevy` crate's Cargo.toml. We are now deploying all of our example assets with the bevy crate. We need to fix this before Bevy 0.8.
