Dist apkcerts.txt in soong

For soong-only builds. This will cause the disted apkcerts to only
contain soong modules, but I think that's ok because unbundled builds
should really only be for soong-built modules.

Bug: 413145177
Test: TARGET_BUILD_APPS=dialer m apps_only dist -k (fails for other reasons but does dist the apkcerts.txt)
Change-Id: I5cb260f2ee60d02e17771db06224690c2869aba9