Remove date from aggregated contributions.

If date is not defined, don't display it.
Lauren got an explicit question from a reporter who thought it meant the number of contributions, not the $ amount.  What is wrong with this change?  I don't understand your statement.

> On Sep 6, 2014, at 1:53 PM, Tom Dooner <notifications@github.com> wrote:
> 
> In views/index.haml:
> 
> > @@ -57,7 +57,7 @@
> >                      <th id='mayoral-table-name-column'></th>
> >                      <th class='mayoral-table-head bold'>Total Raised</th>
> >                      <th class='mayoral-table-head'>Number of itemized contributions</th>
> > -                    <th class='mayoral-table-head'>Percentage of itemized contributions from Oakland*</th>
> > +                    <th class='mayoral-table-head'>Percentage of amount of itemized contributions from Oakland*</th>
> I prefer the previous copy because it seems to me like the natural way to interpret the data, especially given the footnote explaining that it is the percentage of money.
> 
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