Remove php 5.6.23-1+deprecated+dontuse+deb.sury.org~trusty+1
To get rid of the deprecated message, you need to use different ppa: repository.
You have to remove existing packages and the deprecated repository. Then, add the new repository and install the packages you need:
# Remove old ppa: and its packagessudo add-apt-repository ppa:ondrej/php5-5.6 --remove --yessudo apt-get --purge remove php5-common# Add the new ppa:sudo add-apt-repository ppa:ondrej/phpsudo apt-get update# If you are using it with Apache, run:sudo apt-get install libapache2-mod-php5.6# If you are using it with Nginx, run:sudo apt-get install php5.6-fpmSubsequently, you have to make changes to web server configuration, since some paths have changed in the PHP-FPM configuration, etc.
More info here.