remove reference api documentation generation scripts

Looks like some time ago API reference documentation was generated with
Epydoc.
Currently Epydoc project is not maintained (latest release was in 2008),
and trying to build Buildbot docs fails with:

```
Traceback (most recent call last):
  File "apidocs/epyrun", line 202, in <module>
    main()
  File "apidocs/epyrun", line 196, in main
    cli()
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/epydoc/cli.py", line 965, in cli
    main(options, names)
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/epydoc/cli.py", line 757, in main
    exclude_parse=exclude_parse)
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/epydoc/docbuilder.py", line 275, in build_doc_index
    parse_docstring(val_doc, docindex, suppress_warnings)
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/epydoc/docstringparser.py", line 265, in parse_docstring
    api_doc.summary, api_doc.other_docs = api_doc.descr.summary()
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/epydoc/markup/restructuredtext.py", line 179, in summary
    try: self._document.walk(visitor)
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/docutils/nodes.py", line 138, in walk
    if child.walk(visitor):
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/docutils/nodes.py", line 130, in walk
    visitor.dispatch_visit(self)
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/docutils/nodes.py", line 1882, in dispatch_visit
    return method(node)
  File "/home/bob/stuff/buildbot/env/local/lib/python2.7/site-packages/epydoc/markup/restructuredtext.py", line 307, in visit_paragraph
    m = self._SUMMARY_RE.match(child.data)
AttributeError: 'Text' object has no attribute 'data'
```

This can be workarounded by patching Epydoc with patches noted in
common/generate_buildbot_api_documentation.sh (links are broken, but you
can find them on the Internet).

Tickets http://trac.buildbot.net/ticket/2087 and
http://trac.buildbot.net/ticket/1839 refers to the process of migration
docs from API generated to manually-written.

AFAIK Epydoc reference documentation has not been published for the last
few years.

Though IMO autogenerated API docs is pretty good *addition* to manually
written human-readable documentation, current Epydoc configuration is
useless and only confuses.

If we would like to have generated API reference we should investigate
projects such as pydoctor, pdoc, or Sphinx API reference documenting
utilities.

.gitignore

@@ -31,8 +31,6 @@ master/docs/latest
 twisted/plugins/dropin.cache
 .coverage
 coverage-html
-apidocs/reference
-apidocs/reference.tgz
 master/docs/tutorial/_build
 _build
 # tox

Makefile

@@ -1,17 +1,13 @@
 # developer utilities
 
-.PHONY: docs apidocs pylint flake8
+.PHONY: docs pylint flake8
 
 PIP?=pip
 
 # build rst documentation
 docs:
 	$(MAKE) -C master/docs
 
-# create api documentation with epydoc
-apidocs:
-	$(MAKE) -C apidocs
-
 # pylint the whole sourcecode (validate.sh will do that as well, but only process the modified files)
 pylint:
 	$(MAKE) -C master pylint; master_res=$$?; \