Enable `Style/RedundantException` cop and correct offense

.rubocop.yml

@@ -339,6 +339,10 @@ Style/OpMethod:
 Style/ParenthesesAroundCondition:
   Enabled: true
 
+# Checks for an obsolete RuntimeException argument in raise/fail.
+Style/RedundantException:
+  Enabled: true
+
 # Checks for parentheses that seem not to serve any purpose.
 Style/RedundantParentheses:
   Enabled: true

.rubocop_todo.yml

@@ -416,11 +416,6 @@ Style/RaiseArgs:
 Style/RedundantBegin:
   Enabled: false
 
-# Offense count: 1
-# Cop supports --auto-correct.
-Style/RedundantException:
-  Enabled: false
-
 # Offense count: 29
 # Cop supports --auto-correct.
 Style/RedundantFreeze:

app/helpers/preferences_helper.rb

@@ -23,7 +23,7 @@ module PreferencesHelper
 
     if defined.size != DASHBOARD_CHOICES.size
       # Ensure that anyone adding new options updates this method too
-      raise RuntimeError, "`User` defines #{defined.size} dashboard choices," +
+      raise "`User` defines #{defined.size} dashboard choices," \
         " but `DASHBOARD_CHOICES` defined #{DASHBOARD_CHOICES.size}."
     else
       defined.map do |key, _|