run-as: remove a special case.

This is a change for some system apps that have /data/user_de/0/ in the
package list, but it's easier to reason about and more consistent to
always go down the same path.

Bug: http://b/308990322
Test: treehugger
Change-Id: I479485655c61e8a31fb23f779c66d54b0bb476c0