FIX: do not fallback to flair_url column

flair_url is not loaded by our query anymore so avoid falling back
to the old value

app/models/group.rb

@@ -748,7 +748,7 @@ class Group < ActiveRecord::Base
   end
 
   def flair_url
-    flair_icon.presence || flair_upload&.url || self[:flair_url].presence
+    flair_icon.presence || flair_upload&.url
   end
 
   protected

spec/models/group_spec.rb

@@ -972,24 +972,6 @@ describe Group do
     end
   end
 
-  it "allows Font Awesome 4.7 syntax as group avatar flair" do
-    group = Fabricate(:group)
-    group.flair_url = "fa-air-freshener"
-    group.save
-
-    group = Group.find(group.id)
-    expect(group.flair_url).to eq("fa-air-freshener")
-  end
-
-  it "allows Font Awesome 5 syntax as group avatar flair" do
-    group = Fabricate(:group)
-    group.flair_url = "fab fa-bandcamp"
-    group.save
-
-    group = Group.find(group.id)
-    expect(group.flair_url).to eq("fab fa-bandcamp")
-  end
-
   context "Unicode usernames and group names" do
     before { SiteSetting.unicode_usernames = true }