Pretty-printing marker annotations add unnecessary parenthesis

Pretty-printing the AST node for a marker annotation adds unnecessary parenthesis, e.g. `@A` becomes `@A()`.

Fixing this would be a small step towards improving the fidelity of the AST, as discussed in JDK-8024098: "A nice goal/test would be to be able to take a source file, run it through parse() and analyze(), write out the tree, and get the same sequence of tokens found in the original file"