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>

alias.go

@@ -46,7 +46,7 @@ var builtinCmds = map[string]bool{
 	"diff": true, "pull": true, "fetch": true, "push": true, "edit": true,
 	"pushremote": true, "overview": true, "archive": true, "init": true,
 	"login": true, "cd": true, "checkout": true, "clone": true, "cloneall": true,
-	"view": true, "count": true, "tag": true, "alias": true,
+	"count": true, "tag": true, "alias": true,
 	"unalias": true, "config": true, "release": true,
 }