I have Ubuntu 16.04 LTS running with PHP7 and phpmyadmin installed. However, I get a lot of deprecation notices like:
Depre
I had the same problem and none of the solution proposed here worked.
My configuration was Ubuntu 16.04 and php 7.
I solved the issue reinstalling phpmyadmin to last version (5.02). The process is pretty simple. Backup your phpmyadmin folder ('/usr/share/phpmyadmin/' to '/usr/share/phpmyadmin.bak/') by renaming it, create another folder '/usr/share/phpmyadmin/', download the last version of phpmyadmin and copy files inside the newly created folder '/usr/share/phpmyadmin/'. Your version is now upgraded. In my case, deprecation notice vanished.
The process could raise a pair of other errors that you can get rid of by following this guide https://devanswers.co/manually-upgrade-phpmyadmin/