refactor: rename constant LIBZSTD_VERSION_STRING -> ZSTD_VERSION_STRING

Author: kjdev

zstd.c

@@ -1634,7 +1634,7 @@ ZEND_MINIT_FUNCTION(zstd)
     REGISTER_LONG_CONSTANT("ZSTD_VERSION_NUMBER",
                            ZSTD_VERSION_NUMBER,
                            CONST_CS | CONST_PERSISTENT);
-    REGISTER_STRING_CONSTANT("LIBZSTD_VERSION_STRING",
+    REGISTER_STRING_CONSTANT("ZSTD_VERSION_TEXT",
                            ZSTD_VERSION_STRING,
                            CONST_CS | CONST_PERSISTENT);