Remove the completion performance tweak as we no longer use is

resources/default_tweaks.py

@@ -98,15 +98,6 @@
 #   categories_use_field_for_author_name = 'author_sort'
 categories_use_field_for_author_name = 'author'
 
-#: Completion sort order: choose when to change from lexicographic to ASCII-like
-# Calibre normally uses locale-dependent lexicographic ordering when showing
-# completion values. This means that the sort order is correct for the user's
-# language. However, this can be slow. Performance is improved by switching to
-# ascii ordering. This tweak controls when that switch happens. Set it to zero
-# to always use ascii ordering. Set it to something larger than zero to switch
-# to ascii ordering for performance reasons.
-completion_change_to_ascii_sorting = 2500
-
 #: Control partitioning of Tag Browser
 # When partitioning the tags browser, the format of the subcategory label is
 # controlled by a template: categories_collapsed_name_template if sorting by

src/calibre/gui2/complete.py

@@ -16,7 +16,6 @@
 from calibre.utils.icu import sort_key
 from calibre.gui2 import NONE
 from calibre.gui2.widgets import EnComboBox, LineEditECM
-from calibre.utils.config_base import tweaks
 
 class CompleteModel(QAbstractListModel):
 
@@ -27,7 +26,7 @@ def __init__(self, parent=None):
 
     def set_items(self, items):
         items = [unicode(x.strip()) for x in items]
-        if len(items) < tweaks['completion_change_to_ascii_sorting']:
+        if len(items) < 2500:
             self.items = sorted(items, key=sort_key)
             self.sorting = QCompleter.UnsortedModel
         else: