Part of the TMT agreement (from 2015) involved removing some of the telescopes[0]. At least one telescope has been removed (the Caltech Submillimter Observatory, CSO) but aside from the CSO I'm not sure what the status is of other removals. The agreement was that:

> three or four of the mountain’s 13 existing telescopes must be dismantled over the next decade.

This implies the currently agreed upon limit is 10 or 11 telescopes (including the TMT). Unless the agreement has changed, I don't think the promise has been broken since the removal was over the 2015-2025 timescale. That being said, I'm unaware if there was a previous deal.

There had been some controversy in the past regarding "outrigger" telescopes for the 10m Keck telescopes. These would have been used in combination with the 10m telescopes to do interferometry. It was argued that they were thus not "new" telescopes, but rather additions to the existing Keck telescopes. This was controversial and they were never built.

[0] https://www.nature.com/news/hawaii-prunes-mauna-kea-telescop...