Remove humhub\widgets\ModalConfirm for Humhub 1.15

[marc-farre]

The module doesn't work on Humhub 1.15 because of humhub\widgets\ModalConfirm in https://github.com/humhub-contrib/linklist/blob/master/views/linklist/index.php

[yurabakhtin]

@luke- I confirm this module doesn't work with v1.15. I have detected this now while working on the humhub/humhub#6486 (comment).

I find the class humhub\widgets\ModalConfirm was removed here https://github.com/humhub/humhub/pull/6172/files#diff-4d0aaf58071b938d674a161ee566cd927eafb368a97f12adfbd4c4a918a49199. I guess @gevorgmansuryan deleted it because it is not easy to find where the class is used when not all modules are installed in system. Probably we should revert the deletion or try to find another solution for this module.

Also I find a place where the use humhub\widgets\ModalConfirm; still exists in core v1.15 - https://github.com/humhub/humhub/blob/develop/protected/humhub/modules/content/widgets/views/containerProfileImageMenu.php#L6

[luke-]

@yurabakhtin Thanks for the investigation.
@gevorgmansuryan will take a look into this.