Perhaps the easist way to delete these files is to use the Explorer view in the document library.You can use the following url format
http://sharepoint/documents/Forms/WebFldr.aspx , so by addpending "WebFolder.aspx" you will get explorer view and form these you can selectively remove the files. Alternatively you can select "Explorer View" from the drop down present on the top pane of the document library.
Please take note that , its highly recommended that you to take backup of your library first. You can using tools like SPIExplorer at www.codeplex.com/SPIEFolder to do that.
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