Remove superfluous code and quote table name. References #9971 [jkit, nzkoz]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8015 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -442,9 +442,8 @@ module ActiveRecord
 
       # Returns a table's primary key and belonging sequence.
       def pk_and_sequence_for(table) #:nodoc:
-        table_desc_result = execute("describe #{table}")
         keys = []
-        execute("describe #{table}").each_hash do |h|
+        execute("describe #{quote_table_name(table)}").each_hash do |h|
           keys << h["Field"]if h["Key"] == "PRI"
         end
         keys.length == 1 ? [keys.first, nil] : nil