Remove stateUnchanged flag from activity

Bug: 65298313
Test: manual
1) Launch messages
2) Tap on FAB to compose new message, IME shows
3) Tap on Home button
4) Verify IME is hidden

Change-Id: I1823e70d49921d2c66b5abd9ce5d45592bde923c
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 7d65bdc..23bddf6 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -70,7 +70,7 @@
             android:launchMode="singleTask"
             android:clearTaskOnLaunch="true"
             android:stateNotNeeded="true"
-            android:windowSoftInputMode="adjustPan|stateUnchanged"
+            android:windowSoftInputMode="adjustPan"
             android:screenOrientation="nosensor"
             android:configChanges="keyboard|keyboardHidden|navigation"
             android:resizeableActivity="true"