Order the rows
Ctrl+H
Alt+R to toogle Regular Expression Symbol ( .* )
'Search': ^(.*)(\n\1)+$
'Replace with': $1

If the order of lines is important so you can't sort:
'Search': ((^[^\S$]*?(?=\S)(?:.*)+$)[\S\s]*?)^\2$(?:\n)?
In this case, caution:
    Blocks for files with too many lines (1000+) may cause VS Code to crash
    and may introduce blank lines in some cases.