[4.1] gitignore update (#36895)

Post the move to placing css files in the media folder this pr updates the gitignore.

No point in ignoring non-existent files ;)

.gitignore

@@ -22,11 +22,7 @@
 /media
 
 # Template CSS files generated by NPM
-/administrator/templates/atum/css
-/administrator/templates/system/css
 /installation/template/css
-/templates/cassiopeia/css
-/templates/system/css
 
 # Test Related Files
 /phpunit.xml