docs: remove unused helper script

doc/en/_getdoctarget.py

@@ -1,16 +0,0 @@
-#!/usr/bin/env python
-
-import py
-
-def get_version_string():
-    fn = py.path.local(__file__).join("..", "..", "..",
-                                      "_pytest", "__init__.py")
-    for line in fn.readlines():
-        if "version" in line and not line.strip().startswith('#'):
-            return eval(line.split("=")[-1])
-
-def get_minor_version_string():
-    return ".".join(get_version_string().split(".")[:2])
-
-if __name__ == "__main__":
-    print (get_minor_version_string())