[TorchMLIRModule] Drop get_int64_max/min functions

`get_int64_max` and `get_int64_min` was introduced in TorchMLIRModule to
get int64 min/max from C++ standard library and use it as Integer +inf
and -inf. However, the fx_importer now uses torch.iinfo() to get these
values and hence these definitions can be dropped.

python/TorchMLIRModule.cpp

@@ -28,8 +28,4 @@ PYBIND11_MODULE(_torchMlir, m) {
         }
       },
       py::arg("context"), py::arg("load") = true);
-
-  m.def("get_int64_max", []() { return INT64_MAX; });
-
-  m.def("get_int64_min", []() { return INT64_MIN; });
 }