Mech fees on closed column reports duplicate entries

[jmoreira-valory]

Mech fees on closed column reports duplicate entries. Example:

                        Open       Pending    Finalizing   Arbitrating        Closed         TOTAL
--------------------------------------------------------------------------------------------------
Num_trades                 0             0             0             0           878           878
Winner_trades              0             0             0             0           398           398
Num_redeemed               0             0             0             0           367           367
Mech_calls                 0             0             0             0          2791          1448
Investment         0.00 xDAI     0.00 xDAI     0.00 xDAI     0.00 xDAI    64.57 xDAI    64.57 xDAI
Fees               0.00 xDAI     0.00 xDAI     0.00 xDAI     0.00 xDAI     1.32 xDAI     1.32 xDAI
Mech_fees          0.00 xDAI     0.00 xDAI     0.00 xDAI     0.00 xDAI    27.91 xDAI    14.48 xDAI
Earnings           0.00 xDAI     0.00 xDAI     0.00 xDAI     0.00 xDAI    63.62 xDAI    63.62 xDAI
Net_earnings       0.00 xDAI     0.00 xDAI     0.00 xDAI     0.00 xDAI   -30.18 xDAI   -16.75 xDAI
Redemptions        0.00 xDAI     0.00 xDAI     0.00 xDAI     0.00 xDAI    55.20 xDAI    55.20 xDAI
ROI                0.00 %        0.00 %        0.00 %        0.00 %      -32.18 %      -20.84 %   

[jmoreira-valory]

Addressed in #233