You should be able to make use of the Regex Filter to do this.
If you go into the Admin console to the filters and macros section (Spaces -> Settings -> Filters and Macros), you will see the "Regex" filter listed under the section of the page labeled "Filters". If you go into the settings of the Regex Filter you will want to enter in a regular expression to match the text you want filtered in one of the open "Pattern" text boxes and then leave the matching "Replacement Text" text box empty.
Save the changes with the "Save Properties" button and ensure that the Regex filter is set to "On" back on the Filters and Macros page. Clearspace should now replace the pattern you entered with blank in posts.