CNS-434: drop unused fields from subscription proto

proto/subscription/subscription.proto

@@ -6,14 +6,14 @@ option go_package = "github.com/lavanet/lava/x/subscription/types";
 message Subscription {
   string creator = 1; // creator pays for the subscription
   string consumer = 2; // consumer uses the subscription
-  uint64 block = 3; // when the subscription was created
+  uint64 block = 3; // when the subscription was last recharged
   string plan_index = 4; // index (name) of plan
   uint64 plan_block = 5; // when the plan was created
   uint64 duration_total = 6; // total requested duration in months
   uint64 duration_left = 7; // remaining duration in months
-  uint64 month_expiry_time = 8; // expiry time of current month
-  uint64 prev_expiry_block = 9; // when previous month expired
+  reserved 8;
+  reserved 9;
   uint64 month_cu_total = 10; // CU allowance during current month
   uint64 month_cu_left = 11; // CU remaining during current month
-  uint64 prev_cu_left = 12; // CU remaining for previous month
+  reserved 12;
 }