Revert "Added isolate + thread high watermark tracking to Observatory"

runtime/observatory/lib/src/models/objects/thread.dart

Index: runtime/observatory/lib/src/models/objects/thread.dart
diff --git a/runtime/observatory/lib/src/models/objects/thread.dart b/runtime/observatory/lib/src/models/objects/thread.dart
index 7bff72c9191eb98a34a8a0a5a15c7741dee29909..a62353f7b3c88aa0689f8d2a119e03dfa8c87bb7 100644
--- a/runtime/observatory/lib/src/models/objects/thread.dart
+++ b/runtime/observatory/lib/src/models/objects/thread.dart
@@ -20,10 +20,6 @@ abstract class Thread {
   /// The task type associated with the thread.
   ThreadKind get kind;
 
-  /// The maximum amount of memory in bytes allocated by a thread at a given
-  /// time throughout the entire life of the thread.
-  int get memoryHighWatermark;
-
   /// A list of all the zones held by the thread.
   Iterable<Zone> get zones;
 }