Add maxTargetSdk to @UnsupportedAppUsage for mH, mServedView, mNextServedView

These fields are accessed to clean up leaks on older versions,
but they shouldn't be accessed anymore.

Fixes: 123768581
Fixes: 123768639
Fixes: 123769388
Test: no code changes

Change-Id: I7265109290ba11477837bd09136b1d6ef5c73702