Revert "AOSP/Messaging - update the Messaging version to target P (28) or higher. Fixed tests in messagingtests. All tests pass/work."

This reverts commit 9752cda5.

Reason for revert: com.android.devicehealthchecks are failing https://sponge.corp.google.com/target?id=3b9a97f0-48bc-410d-94ce-0971c2f75361&target=com.android.devicehealthchecks&searchFor=&show=FAILED&sortBy=STATUS

Change-Id: I82d337b1d859083169ac6057b408f7e920f06609