Remove storage sandboxes related code.

Bug: 131115422
Test: manual
Test: atest --test-mapping packages/providers/MediaProvider
Test: atest cts/hostsidetests/appsecurity/src/android/appsecurity/cts/ExternalStorageHostTest.java
Test: atest DownloadProviderTests
Test: atest cts/tests/app/src/android/app/cts/DownloadManagerTest.java
Test: atest cts/tests/app/DownloadManagerLegacyTest/src/android/app/cts/DownloadManagerLegacyTest.java
Test: atest cts/tests/app/DownloadManagerApi28Test/src/android/app/cts/DownloadManagerApi28Test.java
Change-Id: Ib3272a47a901ed106474039e72f123b11f5443ff
Merged-In: Ib3272a47a901ed106474039e72f123b11f5443ff