Revert part of 8629b8cee5

As BinGOs noted, all the EUMM testing should be happening in File::Temp
generated tempdirs under cpan/ExtUtils-MakeMaker/t/ so it handles being
run in parallel.

So the fact that lib/Big/(Dummy|Liar).pm are being created on Windows when
building/testing with GCC (but seemingly not MSVC++) is a bug somewhere.