Remove `require 'arel/visitors/bind_visitor'`

This line introduced by the commit fd398475 for using
`Arel::Visitors::BindVisitor`. Currently it is not used.

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

-require 'arel/visitors/bind_visitor'
 require 'active_support/core_ext/string/strip'
 
 module ActiveRecord

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -14,8 +14,6 @@
 require "active_record/connection_adapters/postgresql/utils"
 require "active_record/connection_adapters/statement_pool"
 
-require 'arel/visitors/bind_visitor'
-
 require 'ipaddr'
 
 module ActiveRecord

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

 require 'active_record/connection_adapters/abstract_adapter'
 require 'active_record/connection_adapters/statement_pool'
-require 'arel/visitors/bind_visitor'
 
 gem 'sqlite3', '~> 1.3.6'
 require 'sqlite3'