chore(PythonQt): replace PyString_AS_STRING with PyUnicode_AsUTF8

This removes dependence on the `PyString_*` shim and documents the Python 3
assumption clearly. No functional change intended.

Author: jcfr

src/PythonQt.cpp

@@ -986,7 +986,7 @@ QVariant PythonQt::evalCode(PyObject* object, PyObject* pycode) {
       globals = dict;
     } else {
       dict = PyObject_GetAttrString(object, "__dict__");
-      globals = PyObject_GetAttrString(PyImport_ImportModule(PyString_AS_STRING(PyObject_GetAttrString(object, "__module__"))),"__dict__");
+      globals = PyObject_GetAttrString(PyImport_ImportModule(PyUnicode_AsUTF8(PyObject_GetAttrString(object, "__module__"))),"__dict__");
     }
     PyObject* r = nullptr;
     if (dict) {

src/PythonQtPythonInclude.h

@@ -121,7 +121,6 @@
 #define PY3K
 // Helper defines to facilitate porting
 #define PyString_FromString PyUnicode_FromString
-#define PyString_AS_STRING  PyUnicode_AsUTF8
 #define PyString_AsString   PyUnicode_AsUTF8
 #define PyString_FromFormat PyUnicode_FromFormat
 #define PyString_Check      PyUnicode_Check
@@ -130,7 +129,6 @@
 // Defines to use Python 3 names in Python 2 code
 #define PyBytes_Type      PyString_Type
 #define PyBytes_Check     PyString_Check
-#define PyBytes_AS_STRING PyString_AS_STRING
 #define PyBytes_AsString  PyString_AsString
 #define PyBytes_GET_SIZE  PyString_GET_SIZE
 #define PyBytes_FromStringAndSize PyString_FromStringAndSize