SERVER-14376 Get rid of mongoutils/hash.h.

Move the only function used by the only consumer into the consumer itself.
SERVER-14376 Get rid of mongoutils/README and test.cpp.

The README is no longer true, and the test is neither compiled nor run.
SERVER-14376 Remove mongoutils::checksum, which was only called in one test.
SERVER-14376 Make mongoutils::str available in the mongo namespace.
SERVER-14376 Move mongoutils::html namespace into mongo::html namespace.