Remove unneeded PyErr_Occurred() check in os_lseek_impl() (GH-7557)

This call became unneeded after the posix module was converted to the
Argument Clinic in 2f93635d and should
have been removed as part of that change.

Modules/posixmodule.c

@@ -8238,9 +8238,6 @@ os_lseek_impl(PyObject *module, int fd, Py_off_t position, int how)
     }
 #endif /* SEEK_END */
 
-    if (PyErr_Occurred())
-        return -1;
-
     Py_BEGIN_ALLOW_THREADS
     _Py_BEGIN_SUPPRESS_IPH
 #ifdef MS_WINDOWS