your wallet files are not removed when you uninstall electrum.
anyway what you are proposing is not cold storage. if you are going to do it this way you might as well leave the seeded wallet in place and not bother with a watch-only setup.
what if I delete them manually? yeeh I know it's not a cold storage but trying my best I have cleaned my laptop. I can use live Ubuntu on a USB drive to make it as a cold storage?
A superior method would be to use your Linux live disk to create a new Electrum wallet (remember linux live runs in RAM only and doesn't mark the hard drive). Once the wallet is created then copy the MPK (master public key) to paste on the regular online computer. REMEMBER to write the SEED somewhere so you can always restore the wallet if something goes wrong. This in effect is a true cold wallet approach, although I still like two computers better. Of course you will need to send the BTC from your old wallet to the new one you just created. This is very safe for storage.
Sorry I just noticed that jackg stated the same thing above. Great minds think alike.