Remove complex poll stats

For now we think showing them would be showing too much data and it
would be a bit confusing.

I've been tempted to just remove the view and keep the methods in the
model in case they're used by other institutions using CONSUL. However,
it's probably better to wait until we're asked to re-implement them, and
in the meantime we don't maintain code nobody uses. The code wasn't that
great to start with (I know it because I wrote it).

config/locales/en/stats.yml

@@ -6,8 +6,6 @@ en:
     by_gender: "Participants by gender"
     by_age: "Participants by age"
     by_geozone: "Participants by district"
-    male: "Male"
-    female: "Female"
     men_percentage: "%{percentage} Men"
     women_percentage: "%{percentage} Women"
     age: "Age"
@@ -37,13 +35,7 @@ en:
       heading_disclaimer: "*** Data about headings refer to the heading where each user voted, not necessarily the one that person is registered on."
     polls:
       by_channel: "Participants by channel"
-      by_gender_and_channel: "Participants by gender and channel"
-      by_age_and_channel: "Participants by age and channel"
-      by_geozone_and_channel: "Participants by district and channel"
       vote_by_channel: "Vote type by channel"
-      web: "Web"
-      booth: "Booths"
-      mail: "Mail"
       web_percentage: "%{percentage} Web"
       booth_percentage: "%{percentage} Booths"
       mail_percentage: "%{percentage} Mail"