Disable boost exceptions

There should be no case where we're throwing an exception through an
asio descriptor or through the io_context, so having these options
enabled don't do us much good.

Tested:
Code compiles, removes almost 7kB from the bmcweb binary size.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I91df03fd0dcb942bdfaa420ad8c0c1f8b0f634cc