It's a good idea to use passphrase on SSH key in order to have extra security.
But sometimes you need to remove passphrase from existing SSH key.
Perhaps you need to remove it for automatically pulling from git repository.
Perhaps you need to remove it so it doesn't show on shell history.
It's easy to remove passphrase from ssh key. Just do:
ssh-keygen -p
You'll be asked path to key, old passphrase, and new passphrase. Just enter nothing for new passphrase.