The Tribunal was removed a few years ago as it was backlogged with cases, was inefficient, and was inconsistent in applying punishments. Some players were found to have just been voting "punish" (and some "not punish") for no reason just to get their case load up and make it look like they were helping (in hope of prizes) - leading to the inconsistencies.
The current system is called the Instant Feedback System which is a machine learning algorithm which was trained on corrected Tribunal data (corrected to ensure that the biases above were not a factor). It is more accurate, more consistent, and faster than Tribunal was at issuing punishments to summoners who do not behave. Riot continually audits the system and trains it with new data. For example, if a certain behavior is getting reported a lot, they can train the IFS to be able to detect similar behaviors as toxic. In this way, the community does still regulate itself by either reporting or not reporting behaviors.