cont.c: fix compile error

* cont.c (rb_fiber_t): fix compile error caused by move to
  vm_core.h at r47964.  [Feature #10341]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47969 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
cont.c: fix typedef

* cont.c (rb_fiber_struct): remove useless typedef.
  [Feature #10341]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47970 b2dd03c8-39d4-4d8f-98ff-823fe69b080e