Drop UniqueId from include/v8.h

It's unused since March 2 2017 (https://chromium-review.googlesource.com/448539).
This removes it assuming that leaving it in the header was an oversight.

BUG=v8:5828

Review-Url: https://codereview.chromium.org/2732803002
Cr-Commit-Position: refs/heads/master@{#43605}

include/v8.h

@@ -155,30 +155,6 @@ class GlobalHandles;
 }  // namespace internal
 
 
-/**
- * General purpose unique identifier.
- */
-class UniqueId {
- public:
-  explicit UniqueId(intptr_t data)
-      : data_(data) {}
-
-  bool operator==(const UniqueId& other) const {
-    return data_ == other.data_;
-  }
-
-  bool operator!=(const UniqueId& other) const {
-    return data_ != other.data_;
-  }
-
-  bool operator<(const UniqueId& other) const {
-    return data_ < other.data_;
-  }
-
- private:
-  intptr_t data_;
-};
-
 // --- Handles ---
 
 #define TYPE_CHECK(T, S)                                       \

test/cctest/test-api-interceptors.cc

@@ -38,7 +38,6 @@ using ::v8::String;
 using ::v8::Symbol;
 using ::v8::TryCatch;
 using ::v8::Undefined;
-using ::v8::UniqueId;
 using ::v8::V8;
 using ::v8::Value;
 

test/cctest/test-api.cc

@@ -82,7 +82,6 @@ using ::v8::String;
 using ::v8::Symbol;
 using ::v8::TryCatch;
 using ::v8::Undefined;
-using ::v8::UniqueId;
 using ::v8::V8;
 using ::v8::Value;
 

test/cctest/test-global-handles.cc

@@ -34,7 +34,6 @@
 #include "test/cctest/cctest.h"
 
 using namespace v8::internal;
-using v8::UniqueId;
 
 TEST(EternalHandles) {
   CcTest::InitializeVM();