ci: remove check-ssh-keys (#6136)

ci/check-ssh-keys.sh

@@ -1,4 +0,0 @@
-if grep -q rsa net/scripts/solana-user-authorized_keys.sh; then
-   echo "No rsa keys allowed, small key sizes are insecure."
-   exit 1
-fi

ci/test-sanity.sh

@@ -51,7 +51,6 @@ source ci/_
 
 _ ci/check-channel-version.sh
 _ ci/nits.sh
-_ ci/check-ssh-keys.sh
 
 scripts/increment-cargo-version.sh check