Revert "Add new secure setting for controlling Messaging notifications"

This reverts commit 03da2f00.

 Committer: Tom Taylor <tomtaylor@google.com>

 On branch revertsetting
 Changes to be committed:
   (use "git reset HEAD <file>..." to unstage)

	modified:   api/current.txt
	modified:   core/java/android/provider/Settings.java
	modified:   core/java/android/provider/Telephony.java
	modified:   packages/SettingsProvider/res/values/defaults.xml
	modified:   packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java

We've decided not to disable messaging notifications with a secure setting.
Instead, all the work will be done within the messaging app itself.

Change-Id: Icde6894e76da1007b6026c8ec7dc56e488453c06