dmyenc.c: try to load encdb

* load.c (ruby_require_internal): separate from rb_require_safe,
  not to raise exceptions.
* ruby.c (process_options): remove unnatural encoding search.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48696 b2dd03c8-39d4-4d8f-98ff-823fe69b080e