[libc++] Fix typo in _LIBCPP_REMOVE_TRANSITIVE_INCLUDES (#78639)

Spotted by inspection when trialling out
`_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`. No other instances of `_LIPCPP_`
were found in the repo.

NOKEYCHECK=True
GitOrigin-RevId: f73bf45d68bd2c17602a909751da4a23138d711a

Author: bobsayshilol

include/concepts

@@ -155,7 +155,7 @@ namespace std {
 #include <__config>
 #include <version>
 
-#if _LIBCPP_STD_VER <= 20 && !defined(_LIPCPP_REMOVE_TRANSITIVE_INCLUDES)
+#if _LIBCPP_STD_VER <= 20 && !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES)
 #  include <type_traits>
 #endif
 

include/sstream

@@ -1108,7 +1108,7 @@ _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
-#if _LIBCPP_STD_VER <= 20 && !defined(_LIPCPP_REMOVE_TRANSITIVE_INCLUDES)
+#if _LIBCPP_STD_VER <= 20 && !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES)
 #  include <type_traits>
 #endif