Trade a little weaker test against loplugin:stringconstant

(what prompted writing that very fundamental test now anyway?)

Change-Id: I83884908f8f5b1e4d58575960c77b411183f2fbb

sal/qa/rtl/oustring/rtl_OUString2.cxx

@@ -1001,10 +1001,6 @@ void isEmpty::test() {
 
     aString.clear();
     CPPUNIT_ASSERT_EQUAL_MESSAGE( "aString.clear(), so should now be empty", true, aString.isEmpty() );
-
-    aString = "Not empty any more";
-    aString = "";
-    CPPUNIT_ASSERT_EQUAL_MESSAGE( "aString = \"\", so should now be empty", true, aString.isEmpty() );
 }