Adjust "end namespace" comment in MLIR to match new agree'd coding style

See D115115 and this mailing list discussion:
https://lists.llvm.org/pipermail/llvm-dev/2021-December/154199.html

Differential Revision: https://reviews.llvm.org/D115309

mlir/lib/Bindings/Python/IRCore.cpp

@@ -2012,7 +2012,7 @@ private:
   PyOperationRef operation;
 };
 
-} // end namespace
+} // namespace
 
 //------------------------------------------------------------------------------
 // Populates the core exports of the 'ir' submodule.