DEV: Remove logical OR assignment of constants (#29201)

Constants should always be only assigned once. The logical OR assignment
of a constant is a relic of the past before we used zeitwerk for
autoloading and had bugs where a file could be loaded twice resulting in
constant redefinition warnings.

plugins/poll/db/migrate/20180820080623_migrate_polls_data.rb

@@ -5,9 +5,9 @@ class MigratePollsData < ActiveRecord::Migration[5.2]
     PG::Connection.escape_string(text)
   end
 
-  POLL_TYPES ||= { "regular" => 0, "multiple" => 1, "number" => 2 }
+  POLL_TYPES = { "regular" => 0, "multiple" => 1, "number" => 2 }
 
-  PG_INTEGER_MAX ||= 2_147_483_647
+  PG_INTEGER_MAX = 2_147_483_647
 
   def up
     # Ensure we don't have duplicate polls

plugins/poll/lib/polls_updater.rb

@@ -2,7 +2,7 @@
 
 module DiscoursePoll
   class PollsUpdater
-    POLL_ATTRIBUTES ||= %w[close_at max min results status step type visibility title groups]
+    POLL_ATTRIBUTES = %w[close_at max min results status step type visibility title groups]
 
     def self.update(post, polls)
       ::Poll.transaction do

plugins/poll/plugin.rb

@@ -18,10 +18,10 @@ hide_plugin
 
 after_initialize do
   module ::DiscoursePoll
-    PLUGIN_NAME ||= "poll"
-    DATA_PREFIX ||= "data-poll-"
-    HAS_POLLS ||= "has_polls"
-    DEFAULT_POLL_NAME ||= "poll"
+    PLUGIN_NAME = "poll"
+    DATA_PREFIX = "data-poll-"
+    HAS_POLLS = "has_polls"
+    DEFAULT_POLL_NAME = "poll"
 
     class Engine < ::Rails::Engine
       engine_name PLUGIN_NAME