How to reproduce:
1. Open user's attached "AddressableDoesNotDeleteGeneratedStreamingAssets" project
2. Open Addressables Groups by going to Window->Asset Management->Addressables->Groups
3. At the top of Addressables Group press on Build->New Build->Default Build Script
4. Open Build Settings by going to File->Build Settings...
5. Press Build in the bottom right of the Build Settings window

Expected result: No warnings are thrown
Actual result: A "A meta data file (.meta) exists but its folder 'Assets/StreamingAssets/aa' can't be found" warning is thrown

Reproducible with: 0.0.8-preview, 1.1.10, 1.7.5 (2018.4.20f1, 2019.3.9f1, 2020.1.0b5, 2020.2.0a5)
Could not test with: 2017.4.39f1 because Addressables Package is not introduced

Note: On Addressables version 1.2.4 and earlier 3rd step is Build->Build Player Content instead