Fix some linter warnings

Signed-off-by: Christian Münker <mail@chipmuenk.de>

Author: chipmuenk

pyfda/libs/tree_builder.py

@@ -10,19 +10,11 @@
 Create the tree dictionaries containing information about filters,
 filter implementations, widgets etc. in hierarchical form
 """
-import ast
-from collections import OrderedDict
-import configparser
-import importlib
 import logging
-import os
-# from pprint import pformat
-import re
 import sys
 
 import pyfda.filterbroker as fb
 import pyfda.filter_factory as ff
-import pyfda.libs.pyfda_dirs as dirs
 
 import pyfda.libs.frozendict as frozendict
 

pyfda/libs/widget_class_dicts.py

@@ -11,8 +11,8 @@
 # which have a global scope like class variables.
 
 # -----------------------------------------------------------------------------
-# This file contains dicts with widget class names from the main configuration file, parsed in 
-# `tree_builder._build_widget_class_dicts()`. Those initial definitions are only meant as examples, 
+# This file contains dicts with widget class names from the main configuration file, parsed in
+# `tree_builder._build_widget_class_dicts()`. Those initial definitions are only meant as examples,
 # for documentation and for module test, they are overwritten during the initialization.
 #
 # The keys are the class names of the widgets that have been parsed in the configuration file