Revert "Merge pull request #10539 from davidcelis/ar-sql-improvements"

This reverts commit 257fa689, reversing
changes made to 94725b81.

The build failed

https://travis-ci.org/rails/rails/builds/7883546

activerecord/lib/active_record/relation.rb

@@ -21,7 +21,6 @@ class Relation
     alias :model :klass
     alias :loaded? :loaded
     alias :default_scoped? :default_scoped
-    alias :blank? :empty?
 
     def initialize(klass, table, values = {})
       @klass             = klass
@@ -576,6 +575,11 @@ def with_default_scope #:nodoc:
       end
     end
 
+    # Returns true if relation is blank.
+    def blank?
+      to_a.blank?
+    end
+
     def values
       Hash[@values]
     end