chore(coderd): remove the window option in open_in (#16104)

As we worked on adding a `open_in` parameter for workspace_apps - we
initially created three options :
- window
- slim_window
- tab

After further investigation, `window` should not be used and has to be
removed.

ℹ️ I decided to remove the option instead of deprecating it as we've not
created any release nor documented the feature. Can be discussed.

coderd/apidoc/docs.go

@@ -15346,12 +15346,10 @@ const docTemplate = `{
             "type": "string",
             "enum": [
                 "slim-window",
-                "window",
                 "tab"
             ],
             "x-enum-varnames": [
                 "WorkspaceAppOpenInSlimWindow",
-                "WorkspaceAppOpenInWindow",
                 "WorkspaceAppOpenInTab"
             ]
         },