bpo-38234: Remove _PyPathConfig.dll_path (GH-16307)

The DLL path is not computed from any user configuration and cannot
be configured by PyConfig. Instead, add a new _Py_dll_path global variable.

Remove _PyConfig_SetPathConfig(): replaced with _PyPathConfig_Init().

Py_Initialize() now longer sets the "global path configuration",
but only initialize _Py_dll_path.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index f9ff8f4..e5b6283 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -475,7 +475,7 @@
     config = &interp->config;
 
     if (config->_install_importlib) {
-        status = _PyConfig_SetPathConfig(config);
+        status = _PyPathConfig_Init();
         if (_PyStatus_EXCEPTION(status)) {
             return status;
         }
@@ -646,7 +646,7 @@
     }
 
     if (config->_install_importlib) {
-        status = _PyConfig_SetPathConfig(config);
+        status = _PyPathConfig_Init();
         if (_PyStatus_EXCEPTION(status)) {
             return status;
         }