Topic/remove prefer installer

The "prefer_installer" config option seems to go against current convention to prefer Build.PL when both Build.PL and Makefile.PL are provided in the distribution (some citations below).  The presence of this option detracts from the goal of testing toolchain compliance by including the metadata `configure_requires: { Module::Build(::Tiny)? }` and including a fallback Makefile.PL to warn the user to upgrade his CPAN client.

https://metacpan.org/module/CPAN#CONFIGURATION
https://metacpan.org/module/CPAN::FirstTime

Moreover, it allows a value of "rand" which indescriminately chooses either EUMM or MB.

This was raised via https://rt.cpan.org/Ticket/Display.html?id=89434. It would be a shame to have to remove the warning in Makefile.PL.

Also:

- "Installers should prefer Build.PL when both are available"
  https://rt.cpan.org/Ticket/Display.html?id=32222 and
  https://rt.cpan.org/Ticket/Display.html?id=29235 and
  http://stackoverflow.com/a/3490295/40468
- What to do if both Makefile.PL and Build.PL exist  http://lists.debian.org/debian-perl/2009/05/msg00027.html
- Build.PL vs Makefile.PL http://www.perlmonks.org/?node_id=598631

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