Clean up old composite key code

Because where now supports tuple querying, we don't need to manually
build queries with where and or statements.

activerecord/lib/active_record/associations/collection_association.rb

@@ -64,9 +64,7 @@ def ids_writer(ids)
         ids.map! { |id| pk_type.cast(id) }
 
         records = if klass.composite_primary_key?
-          query_records = ids.map { |values_set| klass.where(primary_key.zip(values_set).to_h) }.inject(&:or)
-
-          query_records.index_by do |record|
+          klass.where(primary_key => ids).index_by do |record|
             primary_key.map { |primary_key| record._read_attribute(primary_key) }
           end
         else

activerecord/lib/active_record/relation/finder_methods.rb

@@ -527,12 +527,7 @@ def find_one(id)
       def find_some(ids)
         return find_some_ordered(ids) unless order_values.present?
 
-        relation = if klass.composite_primary_key?
-          ids.map { |values_set| where(primary_key.zip(values_set).to_h) }.inject(&:or)
-        else
-          where(primary_key => ids)
-        end
-
+        relation = where(primary_key => ids)
         relation = relation.select(table[primary_key]) unless select_values.empty?
         result = relation.to_a
 
@@ -559,11 +554,7 @@ def find_some_ordered(ids)
         ids = ids.slice(offset_value || 0, limit_value || ids.size) || []
 
         relation = except(:limit, :offset)
-        relation = if klass.composite_primary_key?
-          ids.map { |values_set| relation.where(primary_key.zip(values_set).to_h) }.inject(&:or)
-        else
-          relation.where(primary_key => ids)
-        end
+        relation = relation.where(primary_key => ids)
         relation = relation.select(table[primary_key]) unless select_values.empty?
         result = relation.records