Eliminate temREDUNDANT_SEND_MAX (RIPD-590):

The rules for when a SendMax is redundant are complicated. It is easier to always allow a SendMax and eliminate temREDUNDANT_SEND_MAX.

Reviewers: @JoelKatz, @scottschurr 
The change here is really simple and straightforward.  Looks great.  And since this is (apparently) the only place that temREDUNDANT_SEND_MAX is used we can get rid of an error code.  That's nice.

What I'm unsure about are the ramifications.  What did it mean to have a REDUNDANT_SEND_MAX?  What would cause it to fire?  (I'm not precisely sure from reading the code).  Apparently this check was intended to reduce network traffic by declaring this transaction redundant somehow.  How much do we expect network traffic to increase as a result of this change?

Thanks for the additional background.