I am in between developing an roku app, which needs me me save and clear a key d. I am able to do it using roRegistrySection however when I delete the channel, still that key present which should not if I go through the documents which is below
Please advice me how to do it.
It's because you have another app signed with the same developer key on the very same Roku box. Re-read the documentation page you linked to - registry is not unique/isolated "per app" but per "developer ID" - in this way two apps can share a registry if they want to (can be useful at times). And the registry storage will be cleared only when the last such app is deleted.
If this is not a "public" or "private" channel but a "side-loaded" (dev, development channel), you may possibly have to restart Roku for the registry to clear.