file.c: destination path only

* file.c: remove unnecessary the source path from EEXIST error
  messages and show the destination path only.  [ruby-core:59202]
  [Feature #9263]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44313 b2dd03c8-39d4-4d8f-98ff-823fe69b080e