Hi Roberto,
You can't.
However, you can pass the del system command directly in 4GL in a string to be executed or via a .bat/.ps1 file if it is too complex

if you are a partner, I strongly suggest you to use the Eclipse template for Sage X3 Studio from this page:
https://www.sagecity.com/us/sage_erp_x3/sage-x3-global/w/ccoe-tools/3012/safe-x3-studio-eclipse---code-templates-and-snippets

Look for the systemCommand template

in any case, the 4GL instruction system is used:

https://online-help.sageerpx3.com/erp/12/technical-online-help/

https://online-help.sageerpx3.com/erp/12/staticpost/system/

Example extracted from the online help above:

   # Copy FILE1 to FILE2 with stderr redirection on UNIX
    System "cp "+FILE1+" "+FILE2-"2>/dev/null"

   # List of a directory on a Windows server on which the first reference folder is located
   # Returns the list of files and the number of lines read
   # If no directory is given we default it with a temporary directory
    Subprog DIRECTORY_LIST(FILES,DIRECTORY,NUMBER)
    Variable Char FILES(100)(1..)
    Value Char DIRECTORY(100)
    If DIRECTORY="" : DIRECTORY = "C:\sage\tmp" : Endif
    System FILES = adxmac(1)+"@DIR/b/o:n"+DIRECTORY
    NUMBER=stat1
    End

don't forget to specify the machine hostname where you want to delete the files.