Remove remark about password hashing issue being resolved.

There haven't actually been any changes to password hashing around 2.2 or later. The issue described in the linked passage still exists (confirmed with kernel team).

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-952: Explain return values of getLastError

Signed-off-by: Sam Kleinman <samk@10gen.com>