Minor test rearrangement; also test (now) obsolete initial tests for #2066

Author: cowtowncoder

src/test/java/com/fasterxml/jackson/databind/struct/EmptyArrayAsNullTest.java renamed to src/test/java/com/fasterxml/jackson/databind/convert/EmptyArrayAsNullTest.java

@@ -1,4 +1,4 @@
-package com.fasterxml.jackson.databind.struct;
+package com.fasterxml.jackson.databind.convert;
 
 import java.math.BigDecimal;
 import java.math.BigInteger;