dist.ini: Fix Generated Makefile.PL getting pruned.

Unfortunately, Phase order happens as such:

- Add Files.
- Remove Files
- Munge Files
- Finalise Installer

https://metacpan.org/source/RJBS/Dist-Zilla-5.023/lib/Dist/Zilla/Dist/Builder.pm#L317

Which means without this patch, it does:

  GatherDir  ( Imports Makefile.PL from disk )
  MakeMaker  ( Injects a templated Makefile.PL )
  PruneFiles ( Removes both of the above )
  MakeMaker  ( Attempts to munge previously injected Makefile.PL and
      bails when it doesn't exist )

This patch resolves that by removing the problem file before it even
gets added to dzil, eliminating conflict.