With EV3 dropped from the 3.X documentation, the main docs are now nearly identical to the IDE docs, save for some layout changes.
Having just one set of docs is easier to maintain. This drops the IDE doc target.
The doc/api is a legacy name, which is confusing in the current use, since all build targets are now APIs.
Today we have:
doc/common: Common configuration and settings between all targets.
doc/main: Main Pybricks documentation at docs.pybricks.com.
doc/ide: Documentation shipped with the Pybricks Code IDE.