Replace adminer with an active Adminer fork

It seems Adminer doesn't receive frequent updates anymore, the last is from 3 years
ago (vrana/adminer@88647b9).

We now use an active fork (https://github.com/adminerevo/adminerevo, https://docs.adminerevo.org/).
The file was downloaded from https://download.adminerevo.org/4.8.4/adminer/adminer-mysql.zip
instead of the github release as we want to use the file with only MySQL support as its smaller in size.