Change configuration title to just PowerShell (#4063)

The vast majority of other extensions don't add "configuration" to the
prefix, as the text is already displayed under Settings -> Extensions,
and the amount of horizontal space available is small. Since this is
just the title, it is a non-breaking change.

Author: andyleejordan

package.json

@@ -540,7 +540,7 @@
     ],
     "configuration": {
       "type": "object",
-      "title": "PowerShell Configuration",
+      "title": "PowerShell",
       "properties": {
         "powershell.sideBar.CommandExplorerVisibility": {
           "type": "boolean",