You say the document was corrupted, but that need not be so. Find/Replace only looks at the formulæ in the cells or their values, but an external link can occur in various other places, such as in a Named Expression.
To find and remove the link
Open the file as an archive (on Linux: e.g. Ark); open the element content.xml with a text editor; look for file:///. If you find it in a <table:named-range> element, it is a Named Range or Expression; table:name="..." tells you the name; use Sheet|Named Ranges and Expressions to delete that item.