file
PS /home/edward/Desktop>
Get-Content ./copy.txt
[Desktop Entry]
Name=calibre Exec=~/Apps/calibre/calibre
Icon=~/Apps/calibre/resources/content-server/calibre.png
Type=Application*
Start by get the content from file and trim the white spaces if any found in each line of the text document. That becomes the object passed to the where-object to go through the array looking at each member of the array with string length greater then 0. That object is passed to replace the content of the file you started with. It would probably be better to make a new file... Last thing to do is reads back the newly made file's content and see your awesomeness.
(Get-Content ./copy.txt).Trim() | Where-Object{$_.length -gt 0} | Set-Content ./copy.txt
Get-Content ./copy.txt