It is very possible.
Just move the content of the folder to the root level:
If there's a file or subdirectory that has the same name as as one on the root directory, you'll be warned with a message, and it won't be moved. For example, if you have a subdirectory named music, under music itself you'll be warned with this message:
shopt -s dotglob
mv -iv * /path/to/cardroot
In this case you'll have to move it manually with another name:
mv: cannot move `music' to `/path/to/cardroot/music': Directory not empty
To check the directory is absolutely empty run this:
mv -iv /path/to/music/music /path/to/cardroot/othermusic
The expected result should be something like this
ls -la /path/to/music
Then you can even remove music:
drwxrwxr-x 2 youruser youruser 4096 Jun 10 15:27 .
drwxrwxr-x 4 youruser youruser 4096 Jun 10 15:27 ..
That would be it.
rm -rf /path/to/music
Other considerations: Moving your music it may means that your car player might need to rescan all your music again.
Hope it helps. Let us know how it goes.