Don't cleanup sysui test files.

Potentially, cleaning up sysui test files might be causing retries to
fail with module errors, because the retried tests don't have the temp
files they need (they've been deleted). Let's see if this helps fix
b/422328126.

Flag: EXEMPT, test-only change
BUG=422328126

Change-Id: I2f3b1f0b6f80587c7f39ebc63ee4e9628b3fb820