Remove is_provider_enabled() which isn't needed anymore

Re-implement CoverArtProvider.enabled() with a sensible default

See https://github.com/metabrainz/picard/pull/1152/files#r269425834

picard/coverart/providers/__init__.py

@@ -95,15 +95,6 @@ def cover_art_providers():
         yield ProviderTuple(name=p.name, title=p.title, enabled=order[p.name].enabled, cls=p)
 
 
-def is_provider_enabled(provider_name):
-    """Test if provider with name `provider_name` was enabled
-    by user through options"""
-    for name, checked in config.setting['ca_providers']:
-        if name == provider_name:
-            return checked
-    return False
-
-
 class CoverArtProviderMetaClass(type):
     """Provide default properties name & title for CoverArtProvider
     It is recommended to use those in place of NAME and TITLE that might not be defined
@@ -146,14 +137,7 @@ class CoverArtProvider(metaclass=CoverArtProviderMetaClass):
         self.album = coverart.album
 
     def enabled(self):
-        """By default, return True if user enabled the provider
-        through options. It is used when iterating through providers
-        to decide to skip or process one.
-        It can be subclassed to add conditions."""
-        enabled = is_provider_enabled(self.name)
-        if not enabled:
-            log.debug("%s disabled by user" % self.name)
-        return enabled
+        return not self.coverart.front_image_found
 
     def queue_images(self):
         # this method has to return CoverArtProvider.FINISHED or

picard/coverart/providers/caa.py

@@ -544,7 +544,7 @@ class CoverArtProviderCaa(CoverArtProvider):
 
     def enabled(self):
         """Check if CAA artwork has to be downloaded"""
-        if self.coverart.front_image_found:
+        if not super().enabled():
             return False
         if self.restrict_types and not self.len_caa_types:
             log.debug('User disabled all Cover Art Archive types')

picard/coverart/providers/local.py

@@ -71,9 +71,6 @@ class CoverArtProviderLocal(CoverArtProvider):
     _types_split_re = re.compile('[^a-z0-9]', re.IGNORECASE)
     _known_types = set([t['name'] for t in CAA_TYPES])
 
-    def enabled(self):
-        return not self.coverart.front_image_found
-
     def queue_images(self):
         _match_re = re.compile(config.setting['local_cover_regex'], re.IGNORECASE)
         dirs_done = set()

picard/coverart/providers/whitelist.py

@@ -36,9 +36,6 @@ class CoverArtProviderWhitelist(CoverArtProvider):
     NAME = "Whitelist"
     TITLE = N_('Whitelist')
 
-    def enabled(self):
-        return not self.coverart.front_image_found
-
     def queue_images(self):
         self.match_url_relations(('cover art link', 'has_cover_art_at'),
                                  self._queue_from_whitelist)

picard/ui/options/cover.py

@@ -20,7 +20,6 @@
 from picard import config
 from picard.coverart.providers import (
     cover_art_providers,
-    is_provider_enabled,
 )
 
 from picard.ui.checkbox_list_item import CheckboxListItem