Reverts the following commits:

- c81ec6f2:
  "Exposes capture methods to AudioServer, variable renames for
  consistency, added documentation."
- 47c558b9:
  "Expose audio callbacks as signals."
- dabaa11b:
  "Fix to make sure the capture buffers are deallocated at shutdown.
  Silences warnings."

Some documentation improvements were kept for pre-existing methods.

See rationale for reverting these changes in #30468.