Revert "Mention devirtualization in release notes"

Accidental commit. LLVM changes have not been pushed yet
This reverts commit 59245341.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290676 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ReleaseNotes.rst

@@ -47,24 +47,6 @@ sections with improvements to Clang's support for those languages.
 Major New Features
 ------------------
 
-- Enhanced devirtualization with `-fstrict-vtable-pointers`. Clang devirtualizes
-across different basic blocks, like loops:
-
-.. code-block:: c++
-   struct A {
-       virtual void foo() {}
-   };
-   void indirect(A &a, int n) {
-       for (int i = 0 ; i < n; i++)
-           a.foo();
-
-   }
-   void test(int n) {
-       A a;
-       indirect(a);
-   }
-
-
 -  ...
 
 Improvements to Clang's diagnostics