Remove `delayed_commits` setting

[kocolosk]

Documentation of deprecation:

couchdb/test/javascript/tests/delayed_commits.js

Line 16 in 103a062

// test to show it still works. delayed_commits will be removed in 3.0.

[davisp]

@kocolosk In #2208 @nickva did the initial work to remove delayed_settings and I mentioned on that review that we may want to remove fsync_options lest we have people trying to move to disabling those once delayed_commits is gone.

Should we include removing that as part of this you reckon?

[kocolosk]

Good point. I'm OK to remove those options as well.

[davisp]

Cool beans.

[nickva]

Documentation PR if anyone has a change to take a look:

apache/couchdb-documentation#445