[libc++][NFC] Remove stray backtick in documentation

Author: ldionne

libcxx/docs/Hardening.rst

@@ -341,7 +341,7 @@ Vendors can use the following ABI options to enable additional hardening checks:
 
   ABI impact: changes the iterator type of ``vector`` (except ``vector<bool>``).
 
-- ``_LIBCPP_ABI_BOUNDED_UNIQUE_PTR``` -- tracks the bounds of the array stored inside
+- ``_LIBCPP_ABI_BOUNDED_UNIQUE_PTR`` -- tracks the bounds of the array stored inside
   a ``std::unique_ptr<T[]>``, allowing it to trap when accessed out-of-bounds. This
   requires the ``std::unique_ptr`` to be created using an API like ``std::make_unique``
   or ``std::make_unique_for_overwrite``, otherwise the bounds information is not available