Remove unnecessary using directives for WinForms and Drawing in Start-SPMigrationGUI.ps1

Start-SPMigrationGUI.ps1

@@ -1,7 +1,3 @@
-using assembly System.Windows.Forms
-using assembly System.Drawing
-using namespace System.Windows.Forms
-using namespace System.Drawing
 
 [CmdletBinding()]
 param(
@@ -784,6 +780,7 @@ class DialogBuilder : BaseComponent {
     }
 }
 
+# PowerShell 7 can fail to resolve WinForms via `using assembly`, but runtime loading works reliably.
 [void](Add-Type -AssemblyName System.Windows.Forms)
 [void](Add-Type -AssemblyName System.Drawing)
 [System.Windows.Forms.Application]::EnableVisualStyles()