[MM-36444] Manage config deprecations for 6.0 (#18035)

* removing deprecated stuff

* removing deprecations and marking others for deprecations

* removing some of the configs

* partially remove ExperimentalChannelOrganization

* fixing merge issues

* moving default permissions to defaultroles function

* removing experimentaltownsquare

* removing old tests and remove legacysidebar config

* fixing test

* removing log

* removing unused variables

* MM-36444: Fix for renamed functions.

* MM-36444: go mod tidy and go mod vendor.

* MM-36444: Vendored go modules.

* MM-36444: Removes UseExperimentalGossip config field from model.

* Fix vendors

* fixing test

Co-authored-by: Benjamin Cooke <benjamincooke@Benjamins-MacBook-Pro.local>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Martin Kraft <martin@upspin.org>
Co-authored-by: Claudio Costa <cstcld91@gmail.com>

api4/user.go

@@ -57,7 +57,6 @@ func (api *API) InitUser() {
 
 	api.BaseRoutes.User.Handle("/auth", api.APISessionRequiredTrustRequester(updateUserAuth)).Methods("PUT")
 
-	api.BaseRoutes.Users.Handle("/mfa", api.APIHandler(checkUserMfa)).Methods("POST")
 	api.BaseRoutes.User.Handle("/mfa", api.APISessionRequiredMfa(updateUserMfa)).Methods("PUT")
 	api.BaseRoutes.User.Handle("/mfa/generate", api.APISessionRequiredMfa(generateMfaSecret)).Methods("POST")
 
@@ -1510,40 +1509,6 @@ func updateUserAuth(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-// Deprecated: checkUserMfa is deprecated and should not be used anymore, starting with version 6.0 it will be disabled.
-//			   Clients should attempt a login without MFA and will receive a MFA error when it's required.
-func checkUserMfa(c *Context, w http.ResponseWriter, r *http.Request) {
-
-	if *c.App.Config().ServiceSettings.DisableLegacyMFA {
-		http.NotFound(w, r)
-		return
-	}
-
-	props := model.MapFromJSON(r.Body)
-
-	loginId := props["login_id"]
-	if loginId == "" {
-		c.SetInvalidParam("login_id")
-		return
-	}
-
-	resp := map[string]interface{}{}
-	resp["mfa_required"] = false
-
-	if !*c.App.Config().ServiceSettings.EnableMultifactorAuthentication {
-		w.Write([]byte(model.StringInterfaceToJSON(resp)))
-		return
-	}
-
-	if *c.App.Config().ServiceSettings.ExperimentalEnableHardenedMode {
-		resp["mfa_required"] = true
-	} else if user, err := c.App.GetUserForLogin("", loginId); err == nil {
-		resp["mfa_required"] = user.MfaActive
-	}
-
-	w.Write([]byte(model.StringInterfaceToJSON(resp)))
-}
-
 func updateUserMfa(c *Context, w http.ResponseWriter, r *http.Request) {
 	c.RequireUserId()
 	if c.Err != nil {