I\'m trying to remove tinyMCE from a specific textarea that I have created earlier but the following command kept on producing \"undefined\" error (checked using firebug console
You get undefined because in 4.x they removed mceRemoveControl and mceAddControl (I'm not sure about mceFocus) so use mceAddEditor and mceRemoveEditor instead.
Because these codes did the same stuff they removed mceRemoveControl and mceAddControl in the cleanup.
And also don't forget you need to use tinymce in lower case from now.