Make the DIAGNOSTIC_CLEAR permission system|signature like its _READ counterpart

Test: manual
Change-Id: I30f700d0ea1e3712ecacf8f8dd28698adc058158
diff --git a/service/AndroidManifest.xml b/service/AndroidManifest.xml
index 4677cc6..94d039c 100644
--- a/service/AndroidManifest.xml
+++ b/service/AndroidManifest.xml
@@ -92,7 +92,7 @@
       android:description="@string/car_permission_desc_diag_read" />
     <permission
       android:name="android.car.permission.DIAGNOSTIC_CLEAR"
-      android:protectionLevel="dangerous"
+      android:protectionLevel="system|signature"
       android:label="@string/car_permission_label_diag_clear"
       android:description="@string/car_permission_desc_diag_clear" />
     <permission