Remove temporary clean-up from Win32 makefiles

Remove temporary clean-up from Win32 makefiles

Change 22501 temporarily added some clean-up to the Win32 makefiles
which was only meant to stay until cpan rt #5616 was fixed.  It is
now fixed (in EU-MM 6.22, which in turn has been in blead for a
while now), so these hacks are no longer required.

This change is also good for maint, which currently contains EU-MM
6.17, which didn't create the blibdirs.exists files in question
anyway.

p4raw-id: //depot/perl@24347