Fix a regression in ECM mode setting after package install

A 3P package installer can set package source to PACKAGE_SOURCE_STORE to
bypass ECM due to lazy evaluation of ECM state. Revert a previous change
to re-instate ECM mode right after package intallation.

Bug: 349318333
Test: atest EnhancedConfirmationManagerTest
Flag: EXEMPT CVE_FIX
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:c06b539f3109383224362ce9ab567a4c78c383e1
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:30083b50c1f18bf617459e5415da03a29366ea60
Merged-In: Ifffaf8a004d5c7d20ca60c00c487bc4e54899976
Change-Id: Ifffaf8a004d5c7d20ca60c00c487bc4e54899976