Clean up some deprecations & warnings in tests

[Degubi]

• Add some SuppressWarnings("unused") to some fields & classes that are used in reflection code.
• Replace MoreAsserts.assertEquals with Assert.assertArrayEquals.
• Replace primitive wrapper constructor calls with autoboxing or explicit valueOf calls. (Wrapper class constructors deprecated after j9)
• Fix wrong assert imports in MoreAsserts & JsonReaderPathTest.
• Noticed that one of the test methods are failing when using newer java versions in DefaultDateTypeAdapterTest.java, there's already a pr for that: Implemented Fixes suggested by #1432 #1454
• Was thinking about refactoring all the test methods to use the Junit4 @test annotations instead of using the TestCase class