AST: Update documentation comment in SubstitutionMap.h

Author: slavapestov

include/swift/AST/SubstitutionMap.h

@@ -52,11 +52,10 @@ enum class CombineSubstitutionMaps {
 /// any entity that can reference type parameters, e.g., types (via
 /// Type::subst()) and conformances (via ProtocolConformanceRef::subst()).
 ///
-/// SubstitutionMaps are constructed by calling the getSubstitutionMap() method
-/// on a GenericSignature or (equivalently) by calling one of the static
-/// \c SubstitutionMap::get() methods. However, most substitution maps are
+/// SubstitutionMaps are constructed by calling the an overload of the static
+/// method \c SubstitutionMap::get(). However, most substitution maps are
 /// computed using higher-level entry points such as
-/// TypeBase::getMemberSubstitutionMap().
+/// TypeBase::getContextSubstitutionMap().
 ///
 /// Substitution maps are ASTContext-allocated and are uniqued on construction,
 /// so they can be used as fields in AST nodes.