Unexport OmtpMessageReceiver

Introduced in
https://partner-android-review.googlesource.com/#/c/204705/

Receivers do not need to be exported to receive system broadcasts.
OmtpMessageReceiver should also check the intent action, but least
possible scope of change is preferred.

Bug: 31566390
Change-Id: I83f3d42ba185c072357ec6f18b99c3f12f452eb9
(cherry picked from commit a39ff9526aee6f2ea4f6e02412db7b33d486fd7d)
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index b5e3e00..dd3b868 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -656,7 +656,7 @@
             </intent-filter>
         </provider>
         <receiver android:name="com.android.phone.vvm.omtp.sms.OmtpMessageReceiver"
-            android:exported="true">
+            android:exported="false">
             <intent-filter>
                 <action android:name="android.intent.action.DATA_SMS_RECEIVED" />
                 <data android:scheme="sms" />