common.mk: move DEFAULT_PRELUDES

* common.mk (DEFAULT_PRELUDES): no longer configurable since
  r43278, move from Makefile.in and win32/Makefile.sub.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46699 b2dd03c8-39d4-4d8f-98ff-823fe69b080e