Remove greylist of apps that gain legacy access.

Per design pivot, access to legacy behavior will be determined by
the new "allowExternalStorageSandbox" manifest flag.

Bug: 124818022, 129487770
Test: atest --test-mapping packages/providers/MediaProvider
Test: atest android.appsecurity.cts.ExternalStorageHostTest
Change-Id: I169e5eb3612c23aad47204cde9ff263f9df6f8c1