python: remove compile time check for PyString_AsString

The PyString API is specific to Python < 3, replaced by PyBytes and
PyUnicode in Python 3+; hence, drop the compile time check, and use the
right API depending on the Python version.

m4/guestfs-python.m4

@@ -86,18 +86,6 @@ AS_IF([test "x$enable_python" != "xno"],[
             PYTHON_EXT_SUFFIX=$python_ext_suffix
         fi
         AC_MSG_RESULT([$PYTHON_EXT_SUFFIX])
-
-        dnl Look for some optional symbols in libpython.
-        old_LIBS="$LIBS"
-
-        PYTHON_BLDLIBRARY=`$PYTHON -c "import distutils.sysconfig; \
-                                       print (distutils.sysconfig.get_config_var('BLDLIBRARY'))"`
-        AC_CHECK_LIB([c],[PyString_AsString],
-                     [AC_DEFINE([HAVE_PYSTRING_ASSTRING],1,
-                                [Found PyString_AsString in libpython.])],
-                     [],[$PYTHON_BLDLIBRARY])
-
-        LIBS="$old_LIBS"
     fi
 
     AC_SUBST(PYTHON_PREFIX)

python/handle.c

@@ -382,7 +382,7 @@ guestfs_int_py_put_table (char * const * const argv)
 PyObject *
 guestfs_int_py_fromstring (const char *str)
 {
-#ifdef HAVE_PYSTRING_ASSTRING
+#if PY_MAJOR_VERSION < 3
   return PyString_FromString (str);
 #else
   return PyUnicode_FromString (str);
@@ -392,7 +392,7 @@ guestfs_int_py_fromstring (const char *str)
 PyObject *
 guestfs_int_py_fromstringsize (const char *str, size_t size)
 {
-#ifdef HAVE_PYSTRING_ASSTRING
+#if PY_MAJOR_VERSION < 3
   return PyString_FromStringAndSize (str, size);
 #else
   return PyUnicode_FromStringAndSize (str, size);
@@ -402,7 +402,7 @@ guestfs_int_py_fromstringsize (const char *str, size_t size)
 char *
 guestfs_int_py_asstring (PyObject *obj)
 {
-#ifdef HAVE_PYSTRING_ASSTRING
+#if PY_MAJOR_VERSION < 3
   return PyString_AsString (obj);
 #else
   PyObject *bytes = PyUnicode_AsUTF8String (obj);