Revert "checking in the abstractions for valid type checking:"

This reverts commit c321b309a9.

Conflicts:
	activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
	activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

Reason: failing test

  1) Error:
test_valid_column(ActiveRecord::ConnectionAdapters::SQLite3AdapterTest):
NoMethodError: undefined method `column' for
    test/cases/adapters/sqlite3/sqlite3_adapter_test.rb:29:in
`test_valid_column'

activerecord/lib/active_record/schema_dumper.rb

@@ -118,7 +118,7 @@ HEADER
 
           # then dump all non-primary key columns
           column_specs = columns.map do |column|
-            raise StandardError, "Unknown type '#{column.sql_type}' for column '#{column.name}'" unless @connection.valid_type?(column.type)
+            raise StandardError, "Unknown type '#{column.sql_type}' for column '#{column.name}'" if @types[column.type].nil?
             next if column.name == pk
             @connection.column_spec(column, @types)
           end.compact

activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb

@@ -16,15 +16,6 @@ module ActiveRecord
         eosql
       end
 
-      def test_valid_column
-        column = @conn.column('ex').find { |col| col.name == 'id' }
-        assert @conn.valid_type?(column.type)
-      end
-
-      def test_invalid_column
-        assert !@conn.valid_type?(:foobar)
-      end
-
       def test_client_encoding
         assert_equal Encoding::UTF_8, @conn.client_encoding
       end

activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb

@@ -10,15 +10,6 @@ module ActiveRecord
         @connection.exec_query('create table ex(id serial primary key, number integer, data character varying(255))')
       end
 
-      def test_valid_column
-        column = @connection.column('ex').find { |col| col.name == 'id' }
-        assert @connection.valid_type?(column.type)
-      end
-
-      def test_invalid_column
-        assert !@connection.valid_type?(:foobar)
-      end
-
       def test_primary_key
         assert_equal 'id', @connection.primary_key('ex')
       end

activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb

@@ -25,15 +25,6 @@ module ActiveRecord
         @conn.intercepted = true
       end
 
-      def test_valid_column
-        column = @conn.column('items').find { |col| col.name == 'id' }
-        assert @conn.valid_type?(column.type)
-      end
-
-      def test_invalid_column
-        assert @conn.valid_type?(:foobar)
-      end
-
       def teardown
         @conn.intercepted = false
         @conn.logged = []