I was thinking about whether to use DeprecationWarning or TrioDeprecationWarning in #2989, when I decided to actually figure out what the difference is and why TrioDeprecationWarning is a thing. It lines up with https://bugs.python.org/issue24294, which was resolved with https://peps.python.org/pep-0565/ and released in python3.7

Since we don't support 3.6 and earlier, the original reason for its existence is gone, so we at the very least should make it inherit from DeprecationWarning instead of FutureWarning and update the docstring. Or we go even further and remove TrioDeprecationWarning entirely (with an intermediate period of making it a pure alias of DeprecationWarning but emitting a DeprecationWarning).
Having helper methods linking to issues and stuff is still helpful though, and after recent discussions in Gitter we maybe also want a parameter for how long we're planning to keep the deprecated thing around before it gets removed.