Remove ssh key pair generated - Linux

Hi experts, I made a setup ssh key-pairs between two servers.
It worked well, but now I want to delete it.
The problem is that as it is now prompted for authentication locally to the application when trying to run a script for it. For example to run a stop_app, asks me to enter the user password ( should not ).
Here are the steps I did:

server_1:/home/user/> ssh-keygen -t rsa

Select allOpen in new window

I not joined the "passphrase" twice, then 2 files were generated:

id_dsa
id_dsa.pub

Select allOpen in new window

I copied id_dsa_pub to the server_2:

server_1:/home/user/scp id_rsa.pub user@server_2:/home/user/.ssh/

Select allOpen in new window

Prior backup, renamed it id_rsa.pub:

server_2:/home/user/cp -p authorized_keys authorized_keys_bkp
server_2:/home/user/mv id_rsa.pub authorized_keys

Select allOpen in new window

I grant permission to the new file:

server_2:/home/user/chmod 644 authorized_keys

Select allOpen in new window

To try to remove the entries, I tried on both servers:

ssh-keygen -R hostname

Select allOpen in new window

without positive results.
Then, when I returned to the previous file, "autorized_keys", I try:

server_1:/home/user/>ssh user@server_2:/home/user

Select allOpen in new window

I see the message:

ssh server_2:/home/user: Temporary failure in name resolution

Select allOpen in new window

I did not make a backup of known_hosts.
What are the correct steps to roll back the configuration?
Tkankyou in advanced, regards.