[MM-32622] Remove app.WaitForChannelMembership() (#17048)

* Remove app.WaitForChannelMembership

* Fix tests

* Fix test

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/slashcommands/command_invite.go

@@ -4,6 +4,7 @@
 package slashcommands
 
 import (
+	"context"
 	"strings"
 
 	"github.com/mattermost/mattermost-server/v5/app"
@@ -103,7 +104,7 @@ func (*InviteProvider) DoCommand(a *app.App, args *model.CommandArgs, message st
 		}
 	case model.CHANNEL_PRIVATE:
 		if !a.HasPermissionToChannel(args.UserId, channelToJoin.Id, model.PERMISSION_MANAGE_PRIVATE_CHANNEL_MEMBERS) {
-			if _, err = a.GetChannelMember(channelToJoin.Id, args.UserId); err == nil {
+			if _, err = a.GetChannelMember(context.Background(), channelToJoin.Id, args.UserId); err == nil {
 				// User doing the inviting is a member of the channel.
 				return &model.CommandResponse{
 					Text: args.T("api.command_invite.permission.app_error", map[string]interface{}{
@@ -129,7 +130,7 @@ func (*InviteProvider) DoCommand(a *app.App, args *model.CommandArgs, message st
 	}
 
 	// Check if user is already in the channel
-	_, err = a.GetChannelMember(channelToJoin.Id, userProfile.Id)
+	_, err = a.GetChannelMember(context.Background(), channelToJoin.Id, userProfile.Id)
 	if err == nil {
 		return &model.CommandResponse{
 			Text: args.T("api.command_invite.user_already_in_channel.app_error", map[string]interface{}{