Drop dmail filters.

Few people used dmail filters (~900 users in 5 years) and even fewer
used them correctly. Most people used them to try to block dmail spam,
but usually they either blocked too much (by adding common words that
are present in nearly all dmails, causing all mails to them to be
filtered) or too little (blocking specific email addresses or urls,
which usually are never seen again after the spammer is banned).
Nowadays the spam detection system does a better job of filtering spam.

app/views/users/edit.html.erb

@@ -65,13 +65,6 @@
         <%= f.input :disable_responsive_mode, :as => :select, :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false, :hint => "Disable alternative layout for mobile and tablet" %>
         <%= f.input :opt_out_tracking, :as => :select, :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false, :hint => "Opt out of tracking" %>
 
-        <div class="input text optional field_with_hint">
-          <label class="text optional" for="user_dmail_filter_attributes_words">Dmail filter</label>
-          <%= hidden_field_tag "user[dmail_filter_attributes][id]", @user.dmail_filter.try(:id) %>
-          <%= text_field_tag "user[dmail_filter_attributes][words]", @user.dmail_filter.try(:words), :id => "user_dmail_filter_attributes_words", :class => "text optional", :size => 40 %>
-          <span class="hint">A list of banned words (space delimited). Any dmail you receive with a banned word will automatically be deleted.</span>
-        </div>
-
         <%= f.input :favorite_tags, :label => "Frequent tags", :hint => "A list of tags that you use often. They will appear when using the list of Related Tags.", :input_html => { :rows => 5, :data => { :autocomplete => "tag-query" } } %>
         <%= f.input :custom_style, :label => "Custom <a href='https://en.wikipedia.org/wiki/Cascading_Style_Sheets'>CSS</a> style".html_safe, :hint => "CSS rules to apply to the whole site.", :input_html => {:size => "40x5"} %>
       </fieldset>