Remove symbol fields from nodes that don't need them

Symbol is now in the Node superclass, facilitating Nodes being cloneable for the entire copy on write thing, when in reality these are the only nodes that use symbols

20985 [testng] class jdk.nashorn.internal.ir.ObjectNode
1973 [testng] class jdk.nashorn.internal.ir.TernaryNode
53290 [testng] class jdk.nashorn.internal.ir.PropertyNode
*32223 [testng] class jdk.nashorn.internal.ir.VarNode
*231519 [testng] class jdk.nashorn.internal.ir.CallNode
*3798 [testng] class jdk.nashorn.internal.ir.RuntimeNode
* 11642 [testng] class jdk.nashorn.internal.ir.LiteralNode
*32506 [testng] class jdk.nashorn.internal.ir.FunctionNode
*50964 [testng] class jdk.nashorn.internal.ir.IndexNode
*71103 [testng] class jdk.nashorn.internal.ir.AccessNode
*114744 [testng] class jdk.nashorn.internal.ir.UnaryNode
*231651 [testng] class jdk.nashorn.internal.ir.BinaryNode
* 821058 [testng] class jdk.nashorn.internal.ir.IdentNode

(counts in a mandreel run)

We should move symbols into nodes that use them.

Also literals are by virtue of their definitions not in need of symbols, at least not in the traditional typed way - slots maybe