Cleanup and consistency around system server profiling.

The profiling currently works by accident: only because we profile the
boot classpath which executes in JIT zygote do we not load system server
AOT artifacts.

So make the not loading AOT artifacts in system server explicit when the
system server is being profild.

Test: system server profiling
Change-Id: I8d787c8f8524d9d6074dc0f552a856640f11cef0