salhelper: MSVC: pragma warning: make more specific, remove obsolete

Change-Id: I05f1706931612d4d8804cecd860b7195861b1149
Reviewed-on: https://gerrit.libreoffice.org/49043Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

salhelper/qa/test_api.cxx

@@ -121,9 +121,8 @@ void Test::testCondition() {
 }
 
 #ifdef _MSC_VER
-// MSVC 2012 warns about the "p" being unused
-#pragma warning (push, 1)
-#pragma warning (disable: 4189)
+#pragma warning (push)
+#pragma warning (disable: 4189) // 'p': local variable is initialized but not referenced
 #endif