Fix bug #8502, used %PATH% for notepad invocation

We use system %PATH% for notepad executable instead of the absolute
path, because it caused a problem with the migrate script in a 64-bit
meterpreter session. By default the wordpad binary is not in the
%PATH%, so the condition in hp_nnm_ovbuildpath_textfile.rb was not
changed.
Reverting payload_inject because of x64 shellcode

Injecting x64 shellcode in a SYSWOW64 process spawn a 32 bit notepad, so
we revert the changes.
Land #2535 - Use %PATH% for notepad