Also quote extension name in disable_extension

A patch was committed recently which quoted the extension name in the SQL for `enable_extension`. But the same wasn't done for `disable_extension`.
Merge pull request #9687 from stouset/patch-1

Also quote extension name in disable_extension
drop memory consumption and startup speed by switching to define_method
removing out of date comment.  :heart::heart::heart::heart::heart::heart::heart::heart::heart::heart::heart::heart: @pixeltrix