Suppress “Try the new cross-platform PowerShell https://aka.ms/pscore6”

Since Windows Terminal 1.0 is released, you can use it instead.
In settings add a flag -NoLogo as shown below:

    "list": [
  {
    // Make changes here to the powershell.exe profile.
    "guid": "{61c54bd-c2c6-5271-96e7-009a87ff44bf}",
    "name": "Windows PowerShell",
    "commandline": "powershell.exe -NoLogo",
    "hidden": false
  },