Refactor notepad replacement in WinPE

The registry method has proved problematic.  This DOSKEY method seems
less error prone since it's evaluated at runtime.

setup/pe/additions/Program Files/NotepadPlusPlus/npp.cmd

@@ -1,3 +0,0 @@
-@echo off
-
-start "" "%SystemDrive%\Program Files\NotepadPlusPlus\notepad++.exe" %2 %3 %4 %5 %6 %7 %8 %9

setup/pe/additions/Windows/System32/custom.doskey

@@ -1,4 +1,5 @@
+notepad="%ProgramFiles%\NotepadPlusPlus\notepad++.exe" $*
 poweroff=wpeutil shutdown
 reboot=wpeutil reboot
 restart=wpeutil reboot
-shutdown=wpeutil shutdown
+shutdown=wpeutil shutdown

setup/pe/build_pe.ps1

@@ -346,12 +346,6 @@ if ($MyInvocation.InvocationName -ne ".") {
   $Hive.close()
   $RegKey.close()
 
-  # Replace Notepad
-  $RegPath = "HKLM:\WinPE-SW\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\notepad.exe"
-  $NewValue = 'cmd /c "%ProgramFiles%\NotepadPlusPlus\npp.cmd"'
-  New-Item -Path $RegPath -Force | Out-Null
-  New-ItemProperty -Path $RegPath -Name "Debugger" -Value $NewValue -Force | Out-Null
-
   # Run garbage collection to release potential stale handles
   ## Credit: https://jrich523.wordpress.com/2012/03/06/powershell-loading-and-unloading-registry-hives/
   Start-Sleep -Seconds 2