Fix: Remove is_pac column from process_flows.csv

Seems I overlooked this.

Author: alexdewar

examples/simple/process_flows.csv

@@ -1,15 +1,15 @@
-process_id,commodity_id,regions,years,coeff,type,cost,is_pac
-GASDRV,GASPRD,all,all,1.0,fixed,,true
-GASPRC,GASPRD,all,all,-1.05,fixed,,false
-GASPRC,GASNAT,all,all,1.0,fixed,,true
-WNDFRM,ELCTRI,all,all,1.0,fixed,,true
-GASCGT,GASNAT,all,all,-1.5,fixed,,false
-GASCGT,ELCTRI,all,all,1.0,fixed,,true
-RGASBR,GASNAT,all,all,-1.15,fixed,,false
-RGASBR,RSHEAT,all,all,1.0,fixed,,true
-RELCHP,ELCTRI,all,all,-0.33,fixed,,true
-RELCHP,RSHEAT,all,all,1.0,fixed,,false
-GASDRV,CO2EMT,all,all,5.113,fixed,,false
-GASPRC,CO2EMT,all,all,2.5565,fixed,,false
-GASCGT,CO2EMT,all,all,76.695,fixed,,false
-RGASBR,CO2EMT,all,all,58.7995,fixed,,false
+process_id,commodity_id,regions,years,coeff,type,cost
+GASDRV,GASPRD,all,all,1.0,fixed,
+GASPRC,GASPRD,all,all,-1.05,fixed,
+GASPRC,GASNAT,all,all,1.0,fixed,
+WNDFRM,ELCTRI,all,all,1.0,fixed,
+GASCGT,GASNAT,all,all,-1.5,fixed,
+GASCGT,ELCTRI,all,all,1.0,fixed,
+RGASBR,GASNAT,all,all,-1.15,fixed,
+RGASBR,RSHEAT,all,all,1.0,fixed,
+RELCHP,ELCTRI,all,all,-0.33,fixed,
+RELCHP,RSHEAT,all,all,1.0,fixed,
+GASDRV,CO2EMT,all,all,5.113,fixed,
+GASPRC,CO2EMT,all,all,2.5565,fixed,
+GASCGT,CO2EMT,all,all,76.695,fixed,
+RGASBR,CO2EMT,all,all,58.7995,fixed,