Stop using `Arel::Table.engine`

We never actually make use of it on the table, since we're constructing
the select manager manually. It looks like if we ever actually were
grabbing it from the table, we're grossly misusing it since it's meant
to vary by AR class.

Its existence on `Arel::Table` appears to be purely for convenience
methods that are never used outside of tests. However, in production
code it just complicates construction of the tables on the rails side,
and the plan is to remove it from `Arel::Table` entirely. I'm not
convinced it needs to live on `SelectManager`, etc either.

activerecord/lib/active_record/core.rb

@@ -235,7 +235,7 @@ def ===(object)
       #     scope :published_and_commented, -> { published.and(self.arel_table[:comments_count].gt(0)) }
       #   end
       def arel_table # :nodoc:
-        @arel_table ||= Arel::Table.new(table_name, arel_engine)
+        @arel_table ||= Arel::Table.new(table_name)
       end
 
       # Returns the Arel engine.

activerecord/lib/active_record/relation/predicate_builder.rb

@@ -25,7 +25,7 @@ def self.build_from_hash(klass, attributes, default_table)
           if value.empty?
             queries << '1=0'
           else
-            table       = Arel::Table.new(column, default_table.engine)
+            table       = Arel::Table.new(column)
             association = klass._reflect_on_association(column)
 
             value.each do |k, v|
@@ -37,7 +37,7 @@ def self.build_from_hash(klass, attributes, default_table)
 
           if column.include?('.')
             table_name, column = column.split('.', 2)
-            table = Arel::Table.new(table_name, default_table.engine)
+            table = Arel::Table.new(table_name)
           end
 
           queries.concat expand(klass, table, column, value)

activerecord/lib/active_record/relation/query_methods.rb

@@ -858,7 +858,7 @@ def arel # :nodoc:
     private
 
     def build_arel
-      arel = Arel::SelectManager.new(table.engine, table)
+      arel = Arel::SelectManager.new(klass.arel_engine, table)
 
       build_joins(arel, joins_values.flatten) unless joins_values.empty?
 

activerecord/lib/active_record/sanitization.rb

@@ -93,7 +93,7 @@ def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name
         attrs = PredicateBuilder.resolve_column_aliases self, attrs
         attrs = expand_hash_conditions_for_aggregates(attrs)
 
-        table = Arel::Table.new(table_name, arel_engine).alias(default_table_name)
+        table = Arel::Table.new(table_name).alias(default_table_name)
         PredicateBuilder.build_from_hash(self, attrs, table).map { |b|
           connection.visitor.compile b
         }.join(' AND ')