phpBB extension that will not allow the quoting of the last post in a topic.
Clone (or download and move) the repository into the folder ext/tojag/nqlp:
cd phpBB3
git clone https://github.com/rmcgirr83/nqlp.git ext/tojag/nqlp/
Go to "ACP" > "Customise" > "Extensions" and enable the "No quote last post" extension.