Revert "[Runtime][StdLib] Migrate mirrors to use CustomReflectable API, rewrite dump()"

This reverts commit 9798dfd4aa because it
broke the stdlib build.

stdlib/public/core/StringUnicodeScalarView.swift

@@ -29,7 +29,8 @@ public func <(
 extension String {
   /// A collection of [Unicode scalar values](http://www.unicode.org/glossary/#unicode_scalar_value) that
   /// encode a `String` .
-  public struct UnicodeScalarView : CollectionType, CustomStringConvertible, CustomDebugStringConvertible {
+  public struct UnicodeScalarView : CollectionType, _Reflectable,
+    CustomStringConvertible, CustomDebugStringConvertible {
     init(_ _core: _StringCore) {
       self._core = _core
     }
@@ -210,6 +211,12 @@ extension String {
       return Generator(_core)
     }
 
+    /// Returns a mirror that reflects `self`.
+    @warn_unused_result
+    public func _getMirror() -> _MirrorType {
+      return _UnicodeScalarViewMirror(self)
+    }
+
     public var description: String {
       return String(_core[startIndex._position..<endIndex._position])
     }
@@ -406,18 +413,3 @@ extension String.UnicodeScalarIndex {
     return segmenter.isBoundary(gcb0, gcb1)
   }
 }
-
-// Reflection
-extension String.UnicodeScalarView : CustomReflectable {
-  /// Returns a mirror that reflects `self`.
-  @warn_unused_result
-  public func customMirror() -> Mirror {
-    return Mirror(self, children: _MirrorChildrenCollection(underlying: self))
-  }
-}
-
-extension String.UnicodeScalarView : CustomPlaygroundQuickLookable {
-  public func customPlaygroundQuickLook() -> PlaygroundQuickLook {
-    return .Text(description)
-  }
-}