Make Array.indices extension property, move to stdlib

This is not something that needs to be intrinsified. Note that compiler
optimizations are still possible and the fact whether 'indices' is a member or
an extension is irrelevant to the optimizer

generators/src/org/jetbrains/jet/generators/builtins/arrays.kt

@@ -34,8 +34,6 @@ class GenerateArrays(out: PrintWriter) : BuiltInsSourceGenerator(out) {
             out.println()
             out.println("    public fun iterator(): ${s}Iterator")
             out.println()
-            out.println("    public val indices: IntRange")
-            out.println()
             out.println("    public override fun clone(): ${s}Array")
             out.println("}")
             out.println()