Revert "Add read_channel_content permission (#24018)" (#24114)

This reverts commit a19ce047ba.

server/channels/app/webhook.go

@@ -775,7 +775,7 @@ func (a *App) HandleIncomingWebhook(c *request.Context, hookID string, req *mode
 		return model.NewAppError("HandleIncomingWebhook", "web.incoming_webhook.user.app_error", nil, "", http.StatusForbidden).Wrap(result.NErr)
 	}
 
-	if channel.Type != model.ChannelTypeOpen && !a.HasPermissionToChannel(c, hook.UserId, channel.Id, model.PermissionReadChannelContent) {
+	if channel.Type != model.ChannelTypeOpen && !a.HasPermissionToChannel(c, hook.UserId, channel.Id, model.PermissionReadChannel) {
 		return model.NewAppError("HandleIncomingWebhook", "web.incoming_webhook.permissions.app_error", nil, "", http.StatusForbidden)
 	}