[postgres] remove _bc_time_cast_patch.rb, no longer required

It's the same as in Rails 5.1/5.2...and the patch is already gone in 51+.
Plus it redefines apply_seconds_precision() which breaks precision...

Author: dr-itz

lib/arjdbc/postgresql/_bc_time_cast_patch.rb

@@ -682,8 +682,6 @@ class PostgreSQLAdapter < AbstractAdapter
     require 'arjdbc/postgresql/oid_types'
     include ::ArJdbc::PostgreSQL::OIDTypes
 
-    load 'arjdbc/postgresql/_bc_time_cast_patch.rb'
-
     include ::ArJdbc::PostgreSQL::ColumnHelpers
 
     include ::ArJdbc::Util::QuotedCache