This commit removes the implementations of legacy nodes,
their type definitions, and related code that becomes unused.
Now that we have two releases that included the legacy nodes,
there is not much reason to include them still. Removing the
code means refactoring will be easier, and old code doesn't
have to be tested and maintained.
After this commit, the legacy nodes will be undefined in the UI,
so 3.0 or 3.1 should be used to convert files to the fields system.
The net change is 12184 lines removed!
The tooltip for legacy nodes mentioned that we would remove
them before 4.0, which was purposefully a bit vague to allow
us this flexibility. In a poll in a devtalk post showed that the
majority of people were okay with removing the nodes.
https://devtalk.blender.org/t/geometry-nodes-backward-compatibility-poll/20199