Remove USE_EXACT_ALARM

[micahmo]

Pull Request Description

This PR removes the USE_EXACT_ALARM permission to satisfy new Google Play requirements.

• I did not remove the permission from the debug manifest, so we can continue to use more precise alarms for testing. If this still causes issues with Google Play, I can remove it.
• I changed the minimum alarm time to 15 for the background local notification test, and I removed forceAlarmManager. Most likely I didn't really have to change the time since it won't be sooner than 15 minutes anyway, but I figured having that number in the code would at least make things more clear.
• I updated the message that is displayed when the user initiates the background local notification test to indicate that it will likely take around 15 minutes until the notification appears. I also tested it, and this was the case.

Issue Being Fixed

Issue Number: #1532

Screenshots / Recordings

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

LGTM! Thanks for doing this 😄 - I'll let you know if the Google Play build processes properly