Zend: remove zval_dtor() compatibility macro

This is an alias for zval_ptr_dtor_nogc().
I've seen people make mistakes against this and use zval_dtor() instead
of zval_ptr_dtor(). The crucial detail here is that the former won't
root possible GC cycles while the latter will.
We can avoid the confusion by just retiring this compatibility macro.

Closes GH-20235.

UPGRADING.INTERNALS

@@ -32,6 +32,8 @@ PHP 8.6 INTERNALS UPGRADE NOTES
   . ZEND_LTOA() (and ZEND_LTOA_BUF_LEN) has been removed, as it was
     unsafe. Directly use ZEND_LONG_FMT with a function from the
     printf family.
+  . The zval_dtor() alias of zval_ptr_dtor_nogc() has been removed.
+    Call zval_ptr_dtor_nogc() directly instead.
 
 ========================
 2. Build system changes

Zend/zend_variables.h

@@ -81,9 +81,6 @@ ZEND_API void zval_ptr_dtor(zval *zval_ptr);
 ZEND_API void zval_ptr_safe_dtor(zval *zval_ptr);
 ZEND_API void zval_internal_ptr_dtor(zval *zvalue);
 
-/* Kept for compatibility */
-#define zval_dtor(zvalue) zval_ptr_dtor_nogc(zvalue)
-
 ZEND_API void zval_add_ref(zval *p);
 
 END_EXTERN_C()

ext/pdo/pdo_stmt.c

@@ -1052,7 +1052,7 @@ PHP_METHOD(PDOStatement, fetch)
 		array_init_size(return_value, 1);
 		bool success = pdo_do_key_pair_fetch(stmt, ori, off, Z_ARRVAL_P(return_value));
 		if (!success) {
-			zval_dtor(return_value);
+			zval_ptr_dtor_nogc(return_value);
 			PDO_HANDLE_STMT_ERR();
 			RETURN_FALSE;
 		}