Removed an old require of an MD5 digest which is no longer used.
copy-edits RDoc in fba496f

This revision makes the terminology uniform with the rest of the file.
In general we describe these methods in terms of the adapter, rather
than the database. (As a side note, if we wanted to refer to the
database we would write "PostgreSQL".)
Merge pull request #9307 from wangjohn/remove_unneeded_md5_digest

Removed an old require of an MD5 digest which is no longer used.
Add CHANGELOG entry for 41ff6a10216f48f43605a1f9cd6094765cab750f

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