During the normal course of running a CentOS 7 desktop, you will not likely need the extras package repository.
To quickly disable it. First open a terminal and issue the following command and press ENTER.
sudo vim /etc/yum.repos.d/CentOS-Base.repo
Search for the [extras] section. After the line gpgcheck=1 insert the following.
Once done. Save and exit the file.
Update. In the terminal issue the following command and press ENTER.
sudo yum update