Remove sinatra dependency

Not needed anymore with sidekiq 4.2

closes #7153

Gemfile

@@ -34,7 +34,6 @@ gem "simple_captcha2", "0.4.0", require: "simple_captcha"
 # Background processing
 
 gem "sidekiq", "4.2.2"
-gem "sinatra", "1.4.7"
 
 # Scheduled processing
 

Gemfile.lock

@@ -802,10 +802,6 @@ GEM
       json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
-    sinatra (1.4.7)
-      rack (~> 1.5)
-      rack-protection (~> 1.4)
-      tilt (>= 1.3, < 3)
     sinon-rails (1.15.0)
       railties (>= 3.1)
     slop (3.6.0)
@@ -1034,7 +1030,6 @@ DEPENDENCIES
   sidekiq-cron (= 0.4.4)
   simple_captcha2 (= 0.4.0)
   simplecov (= 0.12.0)
-  sinatra (= 1.4.7)
   sinon-rails (= 1.15.0)
   spring (= 2.0.0)
   spring-commands-cucumber (= 1.0.1)