[ci skip] This also removes the unused HAVE_LIBPQ symbol

Author: petk

UPGRADING.INTERNALS

@@ -131,6 +131,7 @@ PHP 8.4 INTERNALS UPGRADE NOTES
    - Symbol HAVE_MYSQL has been removed.
    - Symbol HAVE_PDO_SQLITELIB has been removed.
    - Symbol HAVE_WAITPID has been removed.
+   - Symbol HAVE_LIBPQ has been removed.
    - M4 macro PHP_DEFINE (atomic includes) removed (use AC_DEFINE and config.h).
    - M4 macro PHP_WITH_SHARED has been removed (use PHP_ARG_WITH).
    - M4 macro PHP_STRUCT_FLOCK has been removed (use AC_CHECK_TYPES).