Remove extraneous array wrapping

We're already conditioning `reflection_fk` based on whether it's an
`Array` or not, so no need to wrap it in this `Array()` call since in
this block it is sure to be an `Array`.

Ref.: d7980c6

Author: carlosantoniodasilva

activerecord/lib/active_record/associations/belongs_to_association.rb

@@ -127,7 +127,6 @@ def replace_keys(record, force: false)
           reflection_fk = reflection.foreign_key
           if reflection_fk.is_a?(Array)
             target_key_values = record ? Array(primary_key(record.class)).map { |key| record._read_attribute(key) } : []
-            reflection_fk = Array(reflection.foreign_key)
 
             if force || reflection_fk.map { |fk| owner._read_attribute(fk) } != target_key_values
               reflection_fk.each_with_index do |key, index|