Fix purge bug for program list update

Fix the bug that using keySet and removing items of mPrograms at
the same time during program list update

Bug: 238199883
Test: atest android.hardware.radio.tests.functional
Test: atest com.android.server.broadcastradio.hal2
Change-Id: Ie958b3686780de8c6f3b9912c71dcfe7c07befd0