Remove nil check in Glitch::KeywordMute#=~.

@regex can no longer be nil, so we don't need to check it.

app/models/glitch/keyword_mute.rb

@@ -39,7 +39,7 @@ class Glitch::KeywordMute < ApplicationRecord
     end
 
     def =~(str)
-      regex ? regex =~ str : nil
+      regex =~ str
     end
 
     private