remove app-ephemeral

instant apps are no longer stored in a separate folder. they
are now stored along side other full apps in the apps directory.

Bug: 25119046
Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.EphemeralTest
Change-Id: I6669be797987169a0b9cca78f80539c908812f9e