Simplify CachedAppOptimizer.freezeAppSync variants.

Treat delayMillis=0 as indication that caller wants to
freeze a process immediately.

Bug: 327496592
Test: atest services/tests/mockingservicestests/src/com/android/server/am/ServiceBindingOomAdjPolicyTest.java
Change-Id: I615716baabd955f15129d01b79118a9eb59a250e