Remove unused conditionals from mat-shared-pay.txt

The mat-shared-pay snippet is rendered by the following outcomes:

* outcome_mat-leave_mat-pay_mat-shared-leave_mat-shared-pay
* outcome_mat-leave_mat-pay_pat-leave_both-shared-leave_mat-shared-pay
* outcome_mat-pay_mat-shared-pay
* outcome_mat-pay_pat-leave_pat-shared-leave_mat-shared-pay

These outcomes are all reached from employment_details_of_partner_2b, which can
only be reached from employment_details_of_partner_2a, which in turn can only be
reached if the due date is on or after 5 Apr 2015. This means that the check for
`$IF range_in_2013_2014_fin_year?(due_date)` will never be true.

Author: chrisroos

lib/smartdown_flows/pay-leave-for-parents/snippets/mat-shared-pay.txt

@@ -4,12 +4,6 @@ The mother can get [shared parental pay](/shared-parental-leave-and-pay/overview
 
 ###Amount
 
-$IF range_in_2013_2014_fin_year?(due_date)
-
-Shared Parental Pay (between 6 April 2013 and 5 April 2014) | £136.78 per week or 90% of their average weekly earnings (before tax), whichever is lower
-
-$ENDIF
-
 $IF range_in_2014_2015_fin_year?(due_date)
 
 Shared Parental Pay (between 6 April 2014 and 5 April 2015) | £138.18 per week or 90% of their average weekly earnings (before tax), whichever is lower
@@ -22,7 +16,7 @@ Shared Parental Pay (between 6 April 2015 and 5 April 2016) | £139.58 per week
 
 $ENDIF
 
-$IF NOT range_in_2013_2014_fin_year?(due_date) AND NOT range_in_2014_2015_fin_year?(due_date) AND NOT range_in_2015_2016_fin_year?(due_date)
+$IF NOT range_in_2014_2015_fin_year?(due_date) AND NOT range_in_2015_2016_fin_year?(due_date)
 
 Shared Parental Pay (between 6 April 2015 and 5 April 2016) | £139.58 per week or 90% of their average weekly earnings (before tax), whichever is lower