Remove the view command and the editor setting with it

`view` was the last user of `editor`, so leaving the setting behind would
have made it exactly what `gitkey` was until recently: documented,
parsed, and doing nothing. It is gone from the struct, the template, the
environment, `config -k` and the settings table.

Both names are free for aliases now, as `open` already was.

The tests that used `editor` as their example of a project-overridable
setting use `gitkey` instead, which is the same kind of thing and still
exists.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

show_config.go

@@ -42,7 +42,6 @@ func showConfig() {
 		{"gitname", cfg.GitName},
 		{"gitemail", cfg.GitEmail},
 		{"pushdefault", cfg.PushDefault},
-		{"editor", cfg.Editor},
 		{"mirror", cfg.Mirror},
 		{"secretscan", cfg.SecretScan},
 		{"remotes", cfg.RemoteNames},
@@ -146,7 +145,7 @@ func envName(key string) string { return "MGSH_" + strings.ToUpper(key) }
 func configKeys() []string {
 	keys := []string{
 		"base", "githost", "gitport", "gituser", "gitpath", "gitkey",
-		"gitname", "gitemail", "pushdefault", "editor",
+		"gitname", "gitemail", "pushdefault",
 		"remotes", "mirror", "secretscan",
 	}
 	sort.Strings(keys)