Get rid of unnecessary "rmdir /s" calls in Win32 makefiles

Get rid of unnecessary "rmdir /s" calls in Win32 makefiles

They only existed for the benefit of old shells that didn't
understand "rmdir /s /q", but since change #27195 effectively
drops support for old shells that don't understand "xcopy /y"
it seems unnecessary now.

Windows NT4, 2000, XP and onwards all support "rmdir /s /q", so
it's probably only the Windows 9x shells that lose out.
p4raw-link: @27195 on //depot/perl: b6ed73147a6df30ce6f460cb8d6857100c9a83be

p4raw-id: //depot/perl@27421