Stop shortcutting git.rcjohnstone.com in ssh config

The router resolves it to 10.0.0.2 at the DNS level and the remote URL
already carries :2222, so the alias was redundant everywhere and wrong on
mainframe, where it pointed at localhost. Verified: connecting with
-F /dev/null succeeds from both mainframe and system76.

common/ssh/config

@@ -20,11 +20,3 @@ Host system76
 Host work_laptop
     HostName 10.0.0.8
     User connorjohnstone
-
-# Correct from every machine except mainframe itself, which overrides it in
-# hosts/mainframe/ssh/config.local — there, Gitea is a local port.
-Host git.rcjohnstone.com
-    HostName 10.0.0.2
-    Port 2222
-    User connor
-    IdentityFile ~/.ssh/id_ed25519

hosts/mainframe/ssh/config.local

@@ -1,6 +1,3 @@
-# Gitea runs on this machine; reach it on the loopback rather than out and back.
+# No machine-specific ssh aliases on mainframe.
-Host git.rcjohnstone.com
+# git.rcjohnstone.com is resolved by the router's DNS to 10.0.0.2 and the
-    HostName localhost
+# git remote URL carries :2222, so no alias is needed or wanted here.
-    Port 2222
-    User connor
-    IdentityFile ~/.ssh/id_ed25519