Do not convert StoredDict keys to str.

Instead, convert json keys to int when storage is read.

electrum/json_db.py

@@ -78,16 +78,8 @@ class StoredDict(dict):
         for k, v in list(data.items()):
             self.__setitem__(k, v)
 
-    def convert_key(self, key):
-        """Convert int keys to str keys, as only those are allowed in json."""
-        # NOTE: this is evil. really hard to keep in mind and reason about. :(
-        #       e.g.: imagine setting int keys everywhere, and then iterating over the dict:
-        #             suddenly the keys are str...
-        return str(int(key)) if isinstance(key, int) else key
-
     @locked
     def __setitem__(self, key, v):
-        key = self.convert_key(key)
         is_new = key not in self
         # early return to prevent unnecessary disk writes
         if not is_new and self[key] == v:
@@ -119,24 +111,12 @@ class StoredDict(dict):
 
     @locked
     def __delitem__(self, key):
-        key = self.convert_key(key)
         dict.__delitem__(self, key)
         if self.db:
             self.db.set_modified(True)
 
-    @locked
-    def __getitem__(self, key):
-        key = self.convert_key(key)
-        return dict.__getitem__(self, key)
-
-    @locked
-    def __contains__(self, key):
-        key = self.convert_key(key)
-        return dict.__contains__(self, key)
-
     @locked
     def pop(self, key, v=_RaiseKeyError):
-        key = self.convert_key(key)
         if v is _RaiseKeyError:
             r = dict.pop(self, key)
         else:
@@ -145,11 +125,6 @@ class StoredDict(dict):
             self.db.set_modified(True)
         return r
 
-    @locked
-    def get(self, key, default=None):
-        key = self.convert_key(key)
-        return dict.get(self, key, default)
-