Streaming installation: allow non-v4-signed files (e.g. .dm)

Without this change, we can't install apk-s with dm-s.

Bug: b/150803885
Test: atest PackageManagerShellCommandTest PackageManagerShellCommandIncrementalTest IncrementalServiceTest
Change-Id: I2af87d56560b17f5a5386b55d8d3afb8c6c861f2