Don't allow SdkSandbox to bypass systemUid check.

Test: atest

Flag: EXEMPT security fix

Bug: 397438392
(cherry picked from commit d400709160c8374d83a15dc7623b11434c08c4c6)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:066a09c0c0926d86204898b00640e9969fcba4e3)
Merged-In: I1003ac2a795c869aaeb292692b2681c7a5c8d12e
Change-Id: I1003ac2a795c869aaeb292692b2681c7a5c8d12e