Merge pull request #2864 from nvmkuruc/sdfoptional

Replace `boost::optional` with `std::optional` in `SdfLayer` and `Sdf_TextParserContext`

(Internal change: 2308968)

diff --cc pxr/usd/sdf/layer.h
index 5670e7eda4690e0aba540c25125cbf1f44fb12f6,4c061859f846ac55c45ed75ce1b80e38134c724d..515f258a6cb2cac969c11ead23bdc5a86e60c968
--- 1/pxr/usd/sdf/layer.h
--- 2/pxr/usd/sdf/layer.h
+++ b/pxr/usd/sdf/layer.h
@@@ -48,8 -48,6 +48,7 @@@
  #include <atomic>
  #include <functional>
  #include <memory>
++#include <optional>
  #include <set>
  #include <string>
  #include <vector>

diff --cc pxr/usd/sdf/textParserContext.h
index 7c740820d4abc7af7d247054ede7b8b769cb96c0,85a67822243331fa5d2c12621d735e3d16d8c136..d9bae1ecae3b87f1baa80b91abb3a9e39c998f4b
--- 1/pxr/usd/sdf/textParserContext.h
--- 2/pxr/usd/sdf/textParserContext.h
+++ b/pxr/usd/sdf/textParserContext.h
@@@ -39,8 -39,6 +39,7 @@@
  
  #include "pxr/base/tf/token.h"
  
- #include <boost/optional.hpp>
- 
++#include <optional>
  #include <string>
  #include <vector>