encdb.h.tmpl: remove stale macros

* template/encdb.h.tmpl: remove stale ENCIDX macros which never been
  used, ENCINDEX enums is used.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43364 b2dd03c8-39d4-4d8f-98ff-823fe69b080e