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.