remove py2 remnants and use mocks in tests

fstring wip
Run pyupgrade
fix broken pyupgrade fstring
run pyupgrade on plugin dir
fixup! remove py2 remnants and use mocks in tests
small print bugfix
The file=sys.stderr was part of the format(), so an error got printed to
stdout
Drop use of codecs package
Use builtins.open() instead
fixup! remove py2 remnants and use mocks in tests

jrnl/plugins/jrnl_importer.py

@@ -1,12 +1,10 @@
 #!/usr/bin/env python
 # encoding: utf-8
 
-from __future__ import absolute_import, unicode_literals
-import codecs
 import sys
 from .. import util
 
-class JRNLImporter(object):
+class JRNLImporter:
     """This plugin imports entries from other jrnl files."""
     names = ["jrnl"]
 
@@ -17,15 +15,15 @@ class JRNLImporter(object):
         old_cnt = len(journal.entries)
         old_entries = journal.entries
         if input:
-            with codecs.open(input, "r", "utf-8") as f:
+            with open(input, "r", encoding="utf-8") as f:
                 other_journal_txt = f.read()
         else:
             try:
-                other_journal_txt = util.py23_read()
+                other_journal_txt = sys.stdin.read()
             except KeyboardInterrupt:
-                util.prompt("[Entries NOT imported into journal.]")
+                print("[Entries NOT imported into journal.]", file=sys.stderr)
                 sys.exit(0)
         journal.import_(other_journal_txt)
         new_cnt = len(journal.entries)
-        util.prompt("[{0} imported to {1} journal]".format(new_cnt - old_cnt, journal.name))
+        print("[{} imported to {} journal]".format(new_cnt - old_cnt, journal.name), file=sys.stderr)
         journal.write()