Fix incorrect docstring for powershell.cwd (#4171)

This variable never could have accepted VS Code predefined variables
because support for that is still an open feature request upstream. We
have no API to resolve predefined variables in values given to
contributed settings, and so cannot support this.

Co-authored-by: Patrick Meinecke <SeeminglyScience@users.noreply.github.com>

Author: andyleejordan

package.json

@@ -644,7 +644,7 @@
         "powershell.cwd": {
           "type": "string",
           "default": null,
-          "description": "An explicit start path where the PowerShell Extension Terminal will be launched. Both the PowerShell process and the shell's location will be set to this directory. Predefined variables can be used (i.e. ${fileDirname} to use the current opened file's directory)."
+          "description": "An explicit start path where the PowerShell Extension Terminal will be launched. Both the PowerShell process's and the shell's location will be set to this directory. A fully resolved path must be provided!"
         },
         "powershell.scriptAnalysis.enable": {
           "type": "boolean",