fix(common): BCH, BTG, DGB fix default default_fee_b

- removed unnecessary fee levels. estimated values from blockbook for all levels are the same. "Normal" should be enough.
- long term average BTG fee rate is ~12
- long term average DGB fee rate is ~7

common/defs/bitcoin/bcash.json

@@ -28,10 +28,7 @@
   "fork_id": 0,
   "force_bip143": true,
   "default_fee_b": {
-    "Low": 1,
-    "Economy": 1,
-    "Normal": 1,
-    "High": 100
+    "Normal": 1
   },
   "dust_limit": 546,
   "blocktime_seconds": 600,

common/defs/bitcoin/bgold.json

@@ -28,10 +28,7 @@
   "fork_id": 79,
   "force_bip143": true,
   "default_fee_b": {
-    "Low": 10,
-    "Economy": 70,
-    "Normal": 140,
-    "High": 200
+    "Normal": 30
   },
   "dust_limit": 546,
   "blocktime_seconds": 600,

common/defs/bitcoin/digibyte.json

@@ -28,10 +28,7 @@
   "fork_id": null,
   "force_bip143": false,
   "default_fee_b": {
-    "Low": 10,
-    "Economy": 70,
-    "Normal": 140,
-    "High": 200
+    "Normal": 30
   },
   "dust_limit": 546,
   "blocktime_seconds": 15,