Revert deprecation of `sanitize_sql_hash_for_assignment`

This method is still used by `update_all`

activerecord/CHANGELOG.md

-*   Deprecate `sanitize_sql_hash_for_conditions` and
-    `sanitize_sql_hash_for_assignment` without replacement. Using a `Relation`
-    for performing queries and updates is the prefered API.
+*   Deprecate `sanitize_sql_hash_for_conditions` without replacement. Using a
+    `Relation` for performing queries and updates is the prefered API.
 
     *Sean Griffin*
 

activerecord/lib/active_record/sanitization.rb

@@ -104,9 +104,6 @@ def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name
       #   { status: nil, group_id: 1 }
       #     # => "status = NULL , group_id = 1"
       def sanitize_sql_hash_for_assignment(attrs, table)
-        ActiveSupport::Deprecation.warn(<<-EOWARN)
-sanitize_sql_hash_for_assignment is deprecated, and will be removed in Rails 5.0
-        EOWARN
         c = connection
         attrs.map do |attr, value|
           "#{c.quote_table_name_for_assignment(table, attr)} = #{quote_bound_value(value, c, columns_hash[attr.to_s])}"