You should be able to carry this out in adwords editor fairly easily. View stats for the specified period - order by content clicks. highlight and delete those with no impressions. Not sure if you can do it in the tools section - or whether that is just for search.
Impression for content are not provided on a keyword by keyword basis. This is because ads are not delivered on the content network on the basis of individual keywords, but on the theme of the Ad Group as a hole.
